The best counter to the difficulty getting harder is honestly just being prepared for it with a good team. Nothing is going to save you from the higher difficulties besides solid performance because you will get punished hard and fast for all your mistakes at higher difficulties. I might suggest practicing solo on Hard and Very Hard.
Well, then we have a fun factor barrier. Unfortunately that is a design flaw. My question is, if you get your *** handed to you enough by the AI does the ELO change and does the AI get easier in response? At least then I know the game will notice it's being too rough when I lose over and over and compensate for it, unless they want to drive players away and then of course they don't need to have the AI change. It all just seems counter-intuitive to "fun". I'm hoping the developer responds with whether or not the ELO will effect the AI difficulty in both directions, if so, there really isn't a problem.
In fact, the AI is affected by the ELO of the team and whether or not there's an antagonist. The key idea is to keep giving players a challenge as they progress.
This goes both ways: when you win or lose a match your ELO is affected accordingly, so the AI will be balanced for the next match.
The matchmaking system tries to match players with a similar ELO rating, but this isn't possible all of the times. When this happens, some of the players in the team will find the AI harder than usual and some will find it easier.
Playing in Solo (where you can select AI difficulty) is one way of learning the objectives of each mission and that gives you a chance to assist your team in either situation. When the AI feels harder, try to help the team with levers, buttons, signaling for help or group gathering, or simply being together. When the AI feels easier, try to carry the team through the mission and help the ones that are having a harder time.
Different characters (and their weapons!) can also help with the difficulty. Konstantin, for example, is a great tank with some crowd control when he uses his skill. Harec, on the other hand, is very squishy but deals high amounts of damage.
I hope this helps