Well, floor 5 onwards will have first and 2nd half of the battle, so you need two separate teams, both have to be able to deal enough dmg.

Xingqiu would be the best support for diluc. His ult will always apply hydro for every attack of diluc's so close to 100% vape. Mona.... she's great if you can build the party around her la, otherwise probably razor-kaeya combo is better.

Diluc-XQ can team with bennett, Razor-Kaeya can team with diona. If you wanna use barbara, probably on razor team since diona's heal is not as strong as bennett.

Floor 9/10? Yea, if you dont have a strong healer then everytime the freeze bar almost full then have to run towards the warming thingy & seelie. It'll take a little bit more time, but better than dying I guess

Nope, never too late. Probably great too since you'll have much more content to enjoy with the updates and all. It's a pve focused game, so unless you are somehow competitive with your friends and all, there's really not much that you missed out. At most its just freebies from events, but then again, there will be future events too so...

Tbf, the first abyss season was worse. Floor 10 was a pain especially with pyro carries. Continuously losing HP and crap ton of whooperflowers with so much resistance. Floor 12 with stamina issues. But once you build the team strong enough, you'll kinda outscale it and it becomes just another place to farm.

Floor 9-10 is now sheer cold, which.... does nothing until the bar is full and even then all you need is just a heat source which are just around the room.

Floor 11 was a nightmare at first, but once you learn the AI of the mobs for 11-2, its not bad.

Floor 12 is now in a pretty good spot since its actually harder than 11... unlike the previous version where you dont even need to bother running healers.

Abyss has always been a content for the more hardcore players, which majority of the player base aren't. I personally know a lot who does not go past floor 3 simply because they just enjoy the chill side of the game.