I'm pretty sure this is a shitpost but I'll take the bait and post anyways-
If you remove restrictions from the competitive ruleset the game stops looking anything like traditional competitive formats. Double medic in a game of 6v6 decreases your damage output by 20% in return for double heals, more ubers, and the ability to have 225 HP medics with scout speed. It boggles my mind that froyo didn't look at double med and instantly want to use it, but whatever. Its great, you just have to change some fundemental assumptions about the game. Everyone's life instantly becomes much more important and it turns the game into a numbers game instead of ubers game. Losing one combat class can put your team into a 3v5 in terms of damage potential if the other team isnt mirroring your composition, which can be further exacerbated if you have a class poorly suited to fighting as well (spy, sniper, baby enginner if his buildings die). Ubers stop mattering as much because tracking gets more complicated for a variety of reasons, and you can kinda outheal the damage while kiting if you do it right. Feeding on a combat class generally starts mattering a lot more, and 2019 style soldiers die for their scouts to win tf2 doesn't work (as well, at the very least). Deathball is meta.
On the topic of medics, I also wanna say that the vaccinator is a broken weapon when you have multiple medics. It's not gamebreaking in community competitive formats with just a single medic and is only really useful holding last in that context, but increase the medic count and it snowballs extremely fast into aids territory because it's so easy to always have like 10-20 seconds of 75% damage resistance between your medics to apply however they want in a team fight. People might not realize it rn, but that weapon is potentially the single most broken item in this game if used well.
For the most part the specifics of what you want to run on your team vary based on the map and gametype. A demo is always gonna be a thing, and you want medics as well. Snipers on stopwatch (and maybe koth) are a requirement, but in 5cp you really want scouts for point capping. A second demo is really good in something like gully bc there are only two doors between mid and 2nd. Engineers can abuse the wrangler really well on stopwatch defense. Soldier banners charge at full rate against vaccinator bubbles so it's really easy to farm their charges to combo with ubers (conch + quick fix is devastating bc of the speed boost coupled with knockback negation). Pyros gain an actual niche as a combat class by adding a third damage type against the vaccinator, spy is good for killing snipers because running the razorback in this gamemode is pretty stupid if you can sit with a Darwin's and bullet resist bubbles and be invincible. Double crossbow tanking heavies is a joke and that's actually how my team pushed a couple points on upward scrimming kings crew, we just never did it in our match.
If you actually want my estimation on what a 'best' meta is for this gamemode it's probably something like this-
2 meds (stock + vacc, 2 vacc, 2 quick fix, depending on map)
1 sniper (who should switch on scout in 5cp instead)
Where the flex players should be primarily focusing on scout, soldier, and demo based on map. Engineer and Heavy become staples in stopwatch defense rounds or last holds. Pyro becomes much more useful and really abuseable if your players are smart (You can capture points under vaccinator bubbles. A pyro with a bullet bubble clears your sticks with scorch shot and walks on cap reflecting projectiles, wdyd? Also, upward cliff)
The most aids strategy to come out of playing this format has easily been playing upward, putting a vaccinator med on our sniper, with a stock medic playing normally. The sniper and vacc med literally just stand wherever the fuck they want, kill everything and lower the total amount of fun for the enemy team to 0. Fallen Lord is a sniper main who has never played a single season of esea 6v6 in his life and rolled froyotech + a YouTuber doing this. It is really easy to see that TF2 (outside of the bubble that is esea 6s) has a huge balancing issue in regards to sniper. Take from that what you will.
List of measurably dumb things in this game:
Sticky det bug
Ubers building in pauses
The flamethrower has a negative aim requirement making it stupid with actual damage potential (think jungle inferno pyro)
Engineer is a glorified attachment to his sentry gun
Thanks for listening to my Ted talk
This gamemode is very stupid but it's a nice change of pace and I'm having fun with it.