Well, it's people might be better off under pretty much any parliamentary system but each parliamentary system has its benefits and detriments. No system is really immune though because of ruling classes and culture.

If you want to see what it might have looked like if the USA had been parliamentary all along, Canada might be the best example. Multiple parties, but first past the post, so in any given region it's typically one of two entrenched parties unless people get really pissed. Also, lots of horrendous abuses of First Nations people so not a whole lot better.

Proportional voting parliamentary systems tend towards giving the people what they want most, but their efficacy tends to be based largely on what people want. Consider Israel where the Knesset is proportional: It's permitting a genocide. Simultaneously Germany uses a similar system. Not permitting a genocide but rather enabling one and suppressing the voices of those against enabling a genocide.