If you want "quality discussion", why are you on here and not Tildes? Tildes' whole purpose is quality discussion. Shouldn't you go for the place where that's being optimized for?
Tildes is a great example, actually. They're small and quiet and want to be quiet. They don't want to take off. You can get through Tildes in an hour.
That's why I get bored of Tildes easily. I don't want to just be one-and-done with a site. I want to constantly be discovering new things. I want to see number go up (to an extent). I want to read a bunch of comments, some insightful, some dumb.
If I'm going to post something, I don't want to post it to Tildes. I'll get a slow trickle of comments and replies, people replying to a week-old post with something I've long stopped thinking about.
I worry that if defederation comes and severs the fediverse in two, engagement will go down. Mastodon.social isn't part of the fedipact, and likely won't be. Everywhere that relies on content from Mastodon.social - which is a lot of them, non-techies don't want to find a specific instance - will have a lot less content, very suddenly.
People like me who love refreshing feeds will see the torrent of posts slowly... come... to... a... stop. People like me will get bored - where are all the posts? Why can't I see the creators I really like?
"Well, they're on a server that federates with a server that federates with Meta."
So you'll just be left with those in the fedipact. People who are used to the fast-moving feed (like me) will get frustrated. There's a reason why I left Mastodon in 2019ish and why I left Lemmy in 2020 - they got boring quickly (well, Lemmy was also full of tankies). I left Tildes because it got boring quickly too.
I'm in this sort of industry. I'm not going to reveal much about what I specifically do, but I know that most people want something that is new and exciting and moves fast. It draws them in and causes them to spend most of their time there.
When that feed slows down, they spend less time on that site. When they have enough experiences of "opening the app just to close it again", they'll eventually remove it from their home screen (or bookmarks). Then it gets forgotten about.
When the user forgets about a site, it gets less content. In turn, that makes the content even slower. In turn, that drives more people away, except for the die-hards who love slow discussions (like Tildes or 2019-era Mastodon).
Where are the people who left going to go? Well, they might go to where their creators were - somewhere like Mastodon.social. Or they'll leave entirely, or they'll move to Bluesky or Threads.
A lot of those options aren't healthy for the broader fediverse, so you'll just have this one branch that is dominated by Meta and the other which slowly dies as people leave due to increasingly stale content. If they were united, they might've stood a chance against Meta if/when Meta made an anti-competitive move... but divided they're a lot easier for Meta to scoop up and slowly extinguish, XMPP-style.
Again, the fedipact is doing Meta's dirty work for them.