I dislike the 2-game series as I feel like it generally leads to boring soccer in the first game.It fits the space between season end and the next FIFA break.
Because of MLS competitiveness and HFA, most series go 3 games and fill the entire time period.
The game format in which every tie goes straight to kicks to choose winner/loser is identical to Leagues Cup, yet it seems many people love it in LC and hate it here.
Almost nobody plays for a low scoring draw draw in Game 1.
No matter how bad a blowout in G1, G2 starts even and therefore interesting.
The major negative is nobody else does this in soccer. Fine. I like tradition. But the reasons for 2-game series do not apply here. [Almost] nobody else in soccer has playoffs after a full season. The 180 minute split-contest was invented for tournaments as a way to derive a fair result, and give both teams home gate receipts, while getting done as efficiently as possible. Absent some justification to give 1 team HFA, 2 games make sense. The other alternative is play just one game and to let chance decide who plays at home, which some competitions use at least in some rounds. But both of those options have obvious flaws. Giving 1 team HFA in a single game is basically accepted because of time and schedule constraints and what else you gonna do? But at least it yields a clear winner.*
But 2 game series are absurdly prone to lacking a clear winner, so first they went by goal differential, then they invented the Away Goal Rule, and contests and federations could never agree whether to have Extra Time, or apply the AGR to Extra Time, and then some federations got rid of AGR because it causes arguably as many problems as it solves. In the end, a 2 game series is so inherently flawed that you should never use it except when in a knockout where you both (1) want everyone to get a home game, and (2) nobody deserves HFA. That just does not apply to MLS playoffs.
* Except for those contests where they play the do-over which is ridiculously disruptive and I think I just read the FA is getting rid of it.
Additionally as you pointed out, it's much more balanced which would further make the regular season less meaningful.
I don't mind the 3-game series.