I have just finished the game on easy and I didn’t have any dramatic difficulty spike. It had difficulty level comparable to x-com 2 veteran. I HAVE USED OP class combinations like sniper/heavy, Rally The Troops skill and very late in the game 100% stealth infiltrators. In the late game I had few scavenging missions with high threat level where I managed to secure all the crates.
Before that my first try was on normal difficulty and I failed hard because I didn’t know game mechanics.
My team(s) was primarily snipers (1-2 sniper/heavy, 2-3 sniper/assault) and two scouts (1 assault/heavy, 1 assault/berseker). Later in the game I added priest and infiltrator. With that many snipers and Rally The Troops/ Quick Aim skills it is a lot of firepower in first 2-3 turns.
Basically assault rifles and shotguns become useless very early in the game. I used them only as a secondary weapon to shoot worms because pistols are very inaccurate for that. To shoot something with shotgun you need to be close, and to be close to arthton with 50 hp damage and return fire is a suicide.
Arthrons have a ton of armor but two weak spots are arms. One sniper with quick aim can disable arthron in one turn by shooting off arms. After that if it have spitter head it must come very close to do any harm and then it is easy target for heavy. If not it only jumps around the map useless until it bleeds out.
Tritons with assault rifles or snipers are useless if you disable one of their lower arms because they can’t shoot anymore. If they have tentacles they have to come close to use them and that is heavy’s territory. That is one good sniper shot. After that leave it to roam the map. After you get the priest you can mind control it and take its weapon. This way I got 10-15 sniper rifles.
Sirens mind control is disabled if it gets two sniper shots in the head. After that it can run away or get closer. If it gets closer then heavy deals with it using rage burst.
Mindfragers… do not remove them with pistols as game suggests if controlled soldier has return fire ability, especially if that guy/gal is assault/heavy combo. Use assault rifle instead.
Chiron/Scyla are just nice big targets if you have sniper/heavy with rage burst.
NJ/Synedrion snipers are similar to tritons, if you disable one arm then they can use only pistols. Mind control them to get the gear.
Dynamic difficulty goes wrong
As I mentioned above I heavily used mind control to get snipers/assault rifles/shotguns from tritons. Game adapted to that, in for me funny way, and after some time it started to send only tritons with guns. One time in ambush mission I even got the triton only with mist creating arms with no weapon. Its lower arms were in position like it holds a rifle but there was no rifle. It was an useless enemy. I laughed so hard about that because imo I broke the system.
After all, beside all the bugs and exploits, I had really good time playing this game. I will wait some time for some patches and balancing to play it again on normal difficulty.