Seasonal boosts need to be removed to preserve the game's health.
As you may not know, every characters with the yellow symbol in the selection screen currently has a seasonal boost.
A lot of us thought that these "boost" only occured during a team-up, but that's not the case, they are active during the whole season. Whether that's the +150 HP for Venom, 20% damage for Hawkeye and 15% heals for Cloak&Dagger, they are all ALWAYS active.
And that's very bad, because it means that once all these buffs disappear, everyone is going to feel like their favorite characters got nerfed. Characters that may already be struggling too.
Another reason why it's bad is because it makes it impossible for the community to correctly ask for buffs and nerfs, since we don't have a true vision of the characters. Is Iron Fist actually OP or is it just the seasonal buff ? What if they nerf him on top of the removal of the seasonal bonus next season ?
Same goes for buffs, characters that currently feel slightly underwhelming might get an actual buff AND a seasonal buff next time, making them OP again.
What's the point of learning a character if they're going to be reduced to dust next season ? How can we not feel underpowered when one of our mains doesn't have a seasonal buff while others does ? It's an incomprehensible mechanic that simply shouldn't be in the game as they are currently implemented.
If they only activated with the team-ups, it would be somewhat fine, but having them on all the time is going to kill the meta, forcing people to only ever play buffed characters if they want a chance.