Please read 
I enjoy both but its really cemented why I love dragon age so much more.
These are story based games set in worlds created entirely for these games. Its common to have discussion about how different story events could have gone differently, or what will happen in universe after the events of the most recent installment. Obviously, how these worlds are set up and how the story is told effects the discussions a lot.
In mass effect society spreads across the galaxy and encompasses trillions of individuals across thousands of planets. Despite that, the major story beats hinge on how you treated individual characters, or whether they are alive or not. Like whether an artificial plague causing 99% of krogan pregnancies to miscarry is justified is completely down to whether the good leader is in charge.
Despite trillions of individuals and complex economics all major conflict boils down to species versus species. All krogan, all asari, all turians are just like that so of course this has happened. There are hints in game that there are many different cultures within each species but we get very little evidence of that, and almost entirely in the 3rd game. Krogan (giant toad people with natural armor, anger issues, and a love of violence) are shown to be maybe not inherently violent individuals that care a bit about others, but thats mostly it. We get one pretty butch Asari (otherwise all feminine species).
So when the community talks about these things its always on individualist or species based terms. It is almost impossible to do materialist analysis because of how the games are made. When the community talks about the game arguments are more heated and personal. There are lots more gotcha type lines than in the dragon age community. I suspect this hostile dynamic could contribute to why there are obviously way more women and queer people in the dragon age community.
Mass effect's story is also about exceptional individuals overcoming impossible odds, which lands way better with men, in general, than women, in general.
In the dragon age community discussions revolve around things like, how does the church use drugs to control their private army? How will giving the dwarves a tool that enables them to put their souls into tanks effect their society? How do independent kingdoms respond to a paramilitary organization run by a prophet encroaching on their land?
Mass effect discussions are, "do the volus deserve a council seat?" Instead of, "How could the Volus get a council seat?" or, "How will the volus having a council seat change existing power dynamics?"
Dragon age stories are, "how does magical talent being both random and dangerous effect society?" "Is it worth it to consort with demons to gain power?" Mass effect stories are, "oo ouch owie my magic gives me migraines." (I like Kaiden don't @ me, the whole child soldier bit both games have is nice)
There are other differences too, like dragon age having braver character writing that scares away some of the chuds. Most people on the dragon age subreddit don't like Vivienne, but understand how her inclusion makes the game better. That kind of subelty doesn't exist in mass effect discussions because the game literally wasn't designed for that level of depth. All characters that are apart of your "squad" are meant to be likeable or at least the kind of person their players would respect. Dragon age release characters also in your "squad" like Sera and Vivienne knowing that tons of their players will hate them.
In summary, mass effect is lacking a pair, let alone a quad. (krogan have 4 testicles) (Please laugh I mentioned testicles)
This is underselling ME3 a bit, it was relatively anti-gamer for its time. ME1 and 2 get the 
tho. Even though I like them anyway.
Edit: how could I forget Dragon age has literally actually good trans representation. Theres a FtM guy whos literally just the coolest fighty bro and his dudes respect him.
"So If I grew up under the Qun they'd treat me like a real man?" "You ARE a real man Krem." 
Edit 2: adding data from reddit surveys
The dragon age subreddit is 45.2% women (3.2% trans), 44% men (1.9% trans), 9.1% non binary and 1.7% other. 45.3% Heterosexual
The Mass effect subreddit is 76.4% men (0.6% trans), 19.7% women (1.5% trans), and 6% total trans people. 73.9% hetero
Dragon age reddit 2023 demographics survey: https://docs.google.com/forms/d/1vi-9XTyIx2kvu4hXb309b0NvdWL7Ub_Yj73le6WXzpI/viewanalytics
Mass effect reddit 2019 demographics survey: https://docs.google.com/forms/d/e/1FAIpQLSdNHQxT7COKRuYIaoHBXt0s3DOdq2RgPCLlJg2RCN5pf3kcKA/viewanalytics
The decision to make you work with cerberus was always strange. I think its a symptom of the game only having factions representing, the council. the species central governments, mercenaries/organized crime, and terrorists. But, they gave you a ship and a lot of autonomy. If you accept the in game premise that cerberus is the only faction willing to act against the collectors it becomes easier. But working with cerberus will always feel off. It is nice though if you have Miranda in your party when you blow up the collector base she quits cerberus. Really pisses off TIM.
I didn't finish inquisition on my first playthrough either. It was only after coming back to it that I learned to appreciate it. Now its one of my favorite games ever. I have a post here where I talk about how to get the most out of inqiusition. Depending on your choices in game you can have a pretty satisfying conclusion to the mage rebellion at the end. How would you have done the mage - templar war differently?
I should clarify that it's not that I've played Inquisition once and didn't like it, I've played it like a dozen times with ~250 hours in it, thinking each time that I'll actually like it this time, so I've kinda grown weary of the idea that I actually could at this point haha
For the mage - templar war, like, anything would have been better. It's borderline set dressing the way Inquisition did it. There's barely any context given to what has actually transpired since DA2, and the actual warring factions are just reskinned skyrim bandits in a few places in the Hinterlands. They're just there, they're hostile and you kill them, you don't get to talk to them, or know why they're actually out here fighting. You just wordlessly wipe them out and go talk with the Reasonable Moderates™. Then the entire plotline over just as soon as the game has started, no like ultimate conclusion or victory, no promise of a better future, no rebuilding, just "the Inquisition needed bodies, so we threw a coin and picked a side"
Yeah thats fair. Sorry you've been duped by the game like that. A couple of games have done the same thing to me, fallout 4 being the most prominent example. It sounds like you never got to play trespasser, which would be a huge shame (to me).
I super agree. Most of the actual ground work of the rebellion was laid in supplementary books (that I haven't read). They really should've restructured the plot so that ending the mage rebellion and recruiting your chosen faction would've been the first two acts, instead of only the first act. The plot went in a lot of different directions, which made it unfocused.
I challenge the idea that you work with the reasonable moderates though. Fiona worked for years to make the rebellion happen. The reasonable moderates are people like Vivienne, Wynne, Cassandra. Fiona started a violent revolution to free her people. The ones who you fight are essentially cells that went rogue.
in case you never actually finished inquisition spoiler
you can make leliana the new pope. She legitimizes the free mages in the eyes of the chantry and lets them form their own independent college. She also lets all men and all races take the chantry vows. Previously it was only human women. She also purges super aggressively in most endings lmao. We will make the chantry sunshine and rainbows and I will murder you to make that happen >:(