ikr? its a little exaggerating, especially in the plus version, ♥♥♥♥♥♥♥♥♥ there were so many of them. Normally you already know how many squads are spawned, but with this mod its like just when you think its over - bajam 2 more squads pop out of nowhere and kill your already wounded soldiers. Its a challenge but XCOM has always been a great challenge without any mods. XCOM 2 in particular is exceptionally difficult, and with this mod its not impossible but too difficult to enjoy, just my opinion.

I just get swamped quickly on the first missions with practically fireteams of ADVENT, I had to get a mod that bumps the default size to 6 to spread the attention out between my units.

No, this is in fact impossible. For the number of enemy squads to increase, one would have to modify the Missions themselves, however this Mod merely adds about one enemy into each possible EncounterID. EncounterIDs are placed into each mission and whether they spawn depends on the Difficulty and Force/Alert Level, neither which I modified.

I suppose it might be because I've been pairing this up with custom map mods, and also that i bumped up the difficulty aswell. Just thought it would be something to mention incase anyone else was noticing it.

I noted this kind of problem too and usually was overrun very quickly, but didn't have time to experiment. Today i've saved game before supply raid and turned off IESS. I have maps pack from Vozati and Advent maps pack, and enemy packs - Alien pack from LongWar and Better Advent enemies, alongside with Rulers dlc.
So without IESS it was 4 pods with 3 enemies in each. Then i turned on IESS and reload save, started again supply raid and it was 4 pods with 4 enemies and 5th pod with 3 enemies. Here is the problem sadly :(
By the way, earlier i tried turn off all maps packs i have and test with IESS - 4 enemies in pod with additional pod (some pods stay one on another, i mean toooo close to each other, so it couldn't be as conceived).