So, as a UGC admin I clearly don't have a lot against the league. I played my first season of 6s in UGC while getting carried by some of my really good friends, and then next season decided to try ESEA, which landed me on literally the worst team in Open (we won a total of 8 scrim halves + 1 match (at a scoreline of 2-3) during the course of the entire three months of scrimming four nights a week, two scrims @ 2 halves each night.) So... I know a little bit about getting rolled.
Since that season, I haven't really gone back to UGC. Maybe it's because as an admin I get a taste of the bad shit, but it feels like a much larger proportion of the UGC playerbase is exhaustively chasing the win/loss ratio on the side of their team page instead of actually playing matches and learning from them. Rule-lawyering, post-match ringer denial (i.e. they'd allow a ringer, lose, and the suddenly start looking into the ringer more and suddenly not being ok with it), collecting alts of shitweasels like pokemon, you name it, it has happened. Perhaps the reason it doesn't happen in ESEA is because ESEA simply doesn't care about any of those things, but as a player and a team leader I find that it makes people much more rational and inclined at actually working on creating fair advantages (i.e. player skill and team chemistry), which makes winning and losing a considerably more straight-forward experience. I realize that some of it comes down to just more experience overall (ESEA players tend to have a number of years of competitive experience, vs. UGC players who frequently have little to none and thus have different attitudes towards the meaning of a single win), but I find that ESEA just... teaches players to lose better than UGC does, and in the long run it's more beneficial to both the players, and the scene that they create. Perhaps that difference is partially also on us admins and the rule-set we created, which I readily accept is not flawless. But nonetheless, of the atmospheres of the two leagues, as a player I prefer ESEA, just because of the people involved (and yes, Tri is a treasure and I have no idea how he manages to do it all solo).
On the flipside, yes, the client is an absolute piece of garbage and anyone who's only had issues with it rarely is lucky. I had a teammate one season that would get locked out of the client every match night due to high traffic from his area. When he contacted ESEA they admitted it was a bottleneck on their end and then told him tough titties. I don't think I had a season were at least three matches were not somehow impacted by client issues (on my end, as a team leader - including either client issues for my players, or client issues with the game). That's almost a fifth of the matches, and really isn't acceptable. Unfortunately as a playerbase we don't really have any plausible recourse for the quality issues. If we boycott ESEA, it would be only for ESEA to drop TF2 entirely. I don't necessarily think that has to be disastrous, and I think a good solution will arise rather quickly should that occur. But I don't think anyone wants to attempt it either.
To end the essay, however, I do believe that new players should be given some special considerations when it comes to setting them up for an enjoyable season. I think a lot of us who have been jaded by enough seasons and losses forget how each of those first few wins felt (I'm gonna be honest, my first win in Iron I didn't even realize we won, so focused was I on playing the game), and how important they are to someone who is still shaky and lacks the awareness and experience to pin-point their own mistakes. Learning to lose is crucially important, but... I don't think it's something most people can learn in their first season :x