The sustainable team without having to switch characters often would be 1 main dps, 2 supports and 1 healer. I use diluc(dps), venti and fischl (supports), barbara (healer)
You can use the above in every domain as well.
But in the spiral abyss, you cant do that from the 6th dungeon. Because you would require 2 teams of 4. Unless you have another set of 4 apart from your main 4. Otherwise, you will need to break up your main team to make up for the lack of leveled characters.
So my spiral abyss is only up to 7-1. With the adventurer level of 39.
Strongest team wise, it really depends. Of course having Diluc, venti and jean on the same team would be pretty good. Cus they are 5* dps, support and healer respectively.
But your artifacts and weapons needs leveling too. Thats gonna cost a lot of crystals, lower tier artifacts and mora for you. Dps should obviously get dps artifacts like attack boost or element dmg (eg. % fire dmg). Healers could get the Maidan’s artifacts for the healing. Supports is really up to you.
Overall you dont really need the best of the best units unless you want a much easier way of clearing spiral abyss or just regular mob clearing.
Then again, its a gacha game so the chances of a 5 star unit is legendary rare. But the rates on genshin impact is much better than epic seven. I got diluc on the second discounted noelle roll. And venti on the second roll on the venti banner. So im just lucky.
Well other than that, lets all look forward to update 1.1 coming in November