I feel it was banned because of how players were "supposed" to use it had it remained.
It wasn't about it being used full-time. It was about how teams would have to play if they wanted to do things optimally
Playing in EU with the vaccinator and quickiebombs resulted in the following scenarios:
- Teams would wipe on mid, respawn with vaccinator on last with full disad, and still get vaccinator ubers. A direct upgrade when the other choice is 30% uber when they use into you
- Quickiebombs were often better when pushing last. You'd prefire a door/shutter to clear stickies so it'd be safe to milk longer and then you'd shoot a sticky on point
Having a medic be comfortable with vaccinator switches would save you a couple lost rounds throughout a season. And if you were preparing a last push you should consider switching to quickies first. TF2 players figured out these meta shifts quite quickly tbh. But very few people actually wanted to do this because it felt like shit to do so. So most didn't and chose to play "sub-optimally"
Also, switching loadouts is clunky. It's a pain to do so even with binds or the quickswitch menu.
In case of quickiebombs it requires someone to die to switch (you probably play stock stickies for mid still)
Switch to loadout, remember to switch back next life.
Are item servers working properly tonight?
etc