Does it drag during the first run or only on repeat playthroughs?

It's fine on the first run, but drags on subsequent runs. It doesn't help that the first half of the game is identical for each of the 4 routes. The units are also extremely customizable, in a way that they feel more like Final Fantasy Tactics units instead of Fire Emblem. This is generally good, but I get choice paralysis pretty bad so it makes me hesitant on replays.

I played Echoes for the first time earlier this year and loved it despite some of its quirks and deviations from the formula. Probably the best presentation in the series too imo. I wouldn't mind if other JP-only games got the same treatment.

Echoes is fantastic, but sold like crap, unfortunately. I'd love a Genealogy of the Holy War with some QoL improvements, but I'm not holding my breath tbh. Luckily all of the Japan-only games have solid fan translations, and you can use emulator savestates/fast-forwards to get some of the QoL stuff the original releases need. I'd definitely recommend giving them a shot if you haven't played them already.