I think the main problem with Terastal is just how volatile the mechanic is. Terastal is tantalizingly within the realm of manageability...on paper.
In practice, you've got six Pokemon to a team that can each be running one of several different Tera Types that could significantly increase their power level or upend their matchup spread on a dime. Possibly both. No, not every Pokemon is gonna use all 18 Tera types, but nearly every Pokemon's got their STABs and at least a couple defensive/extra STAB options that can each drastically change how you deal with them. This is on top of the usual variance that comes with EV Spreads, Items and Moves.
It's really not a matter of information; Pokemon is, in some part, a game of gleaning information out of your opponent. It's the fact that this particular bit of information, known or not, adds a whole other dimension to trying to play around an opponent. Even if you added Tera Types to Team Preview and could even reasonably guess which of your opponent's Pokemon was gonna style it up, you still have to account for the fact that your opponent can either makeshift-Adaptability their way through you or possibly turn off your checks by changing their type altogether.
Terastal might not be the obvious stupid power buff of Dynamax, but they're both broken in similar ways. Both of them make the game incredibly volatile and prone to massive swings. Dynamax's swings were bigger, but Terastal's are more pervasive and flexible. In either case, the game devolves into people either using the most broken Hyper Offense they can think of to abuse the mechanic (until those things get punted upstairs and the next-best-things step up) or the few strictly defensive Pokemon that can somewhat consistently weather the storm.
I realize fun is subjective, but I don't see how a meta with a mechanic so powerful it encourages such binary play is any more fun than a meta where it's not there and a wider range of strategies can potentially take root. Is Terastal emblematic of the generation? Sure, maybe in VGCs where TPCi actually gives something resembling a fuck about the competitive scene. The developers already don't care what we're doing; they wouldn't have mandated the stupid 20 minute timer or removed 100-All battles if they did. So why are some players tethering themselves to the notion that we should care about preserving what the developers did to the game? We're here to inject order into chaos, essentially, not sit amongst the chaos and say "Welp, that's just how it is."
I know it's a generational gimmick and we need to humour the idea of keeping it around in some capacity anyway, but I'd just get it over with and ban the mechanic. It's too chaotic for its own good.
In practice, you've got six Pokemon to a team that can each be running one of several different Tera Types that could significantly increase their power level or upend their matchup spread on a dime. Possibly both. No, not every Pokemon is gonna use all 18 Tera types, but nearly every Pokemon's got their STABs and at least a couple defensive/extra STAB options that can each drastically change how you deal with them. This is on top of the usual variance that comes with EV Spreads, Items and Moves.
It's really not a matter of information; Pokemon is, in some part, a game of gleaning information out of your opponent. It's the fact that this particular bit of information, known or not, adds a whole other dimension to trying to play around an opponent. Even if you added Tera Types to Team Preview and could even reasonably guess which of your opponent's Pokemon was gonna style it up, you still have to account for the fact that your opponent can either makeshift-Adaptability their way through you or possibly turn off your checks by changing their type altogether.
Terastal might not be the obvious stupid power buff of Dynamax, but they're both broken in similar ways. Both of them make the game incredibly volatile and prone to massive swings. Dynamax's swings were bigger, but Terastal's are more pervasive and flexible. In either case, the game devolves into people either using the most broken Hyper Offense they can think of to abuse the mechanic (until those things get punted upstairs and the next-best-things step up) or the few strictly defensive Pokemon that can somewhat consistently weather the storm.
I realize fun is subjective, but I don't see how a meta with a mechanic so powerful it encourages such binary play is any more fun than a meta where it's not there and a wider range of strategies can potentially take root. Is Terastal emblematic of the generation? Sure, maybe in VGCs where TPCi actually gives something resembling a fuck about the competitive scene. The developers already don't care what we're doing; they wouldn't have mandated the stupid 20 minute timer or removed 100-All battles if they did. So why are some players tethering themselves to the notion that we should care about preserving what the developers did to the game? We're here to inject order into chaos, essentially, not sit amongst the chaos and say "Welp, that's just how it is."
I know it's a generational gimmick and we need to humour the idea of keeping it around in some capacity anyway, but I'd just get it over with and ban the mechanic. It's too chaotic for its own good.