Worgen said:
At the point I'm at now, they are still dangerous because of those crits, but not deadly because I've got better tech and a leveled team. Really the big mistake I made at first was researching weapons before armor. I lost a lot of guys before they started toughening up.
I'm playing CI and have wiped two campaigns on the same Thin Man mission (the introduction to Exalt). First time it was a mix of veterans and rookies, 2nd time it was all veterans with more or less an identical result (a 9 point crit is a 9 point crit, rookie or vet). I hadn't even gotten close to the first armor tier, research wise, I'm still basically in month 1.
Thin Men always represented the only real difficulty spike in the game, apart from possibly Sectopods and Mind Control, and it's demonstrably worse now with aiming angles. The only way to mitigate their extraordinarily high accuracy at the time they appear was full cover/smoke, and now they just angle you and get massive flanking bonuses to hit and crit. If I had to guess, I'd say no Thin Man will ever shoot at you with less than 80% accuracy barring improved smoke.