Behold the problem with this mod. The fanbase is a bunch of tough guys who respond to all notes of difficulty with "Well I can do it, so you need to get better!" while simultaniously posting on the discord about how everything is too easy so it needs buffed. This is exactly why Devourer of Gods is often posted about, all its weaknesses were patched out because these guys keep saying it's too easy to do x strategy, and now it's all but unthinkable for a blind player to approach.
...Still, part of this is intentional. Drew has stated a number of times that his bosses are supposed to be harder than vanilla ones, and that they follow their own difficulty scaling. Expect to run into this a lot, Cryogen's going to be a harder kill than any mech, and if you think you're bagging Calamitas before Plantera without a ton of prep and plan, you'd best get to the prepping and planning, because THAT ain't happening.
I also believe Calamity's bosses don't scale like vanilla as far as expert/normal goes. The Normal mode fights are only slightly weaker than the expert variations, so in normal mode the power gap is even MORE pronounced, AND you don't get the boosted defense effect you otherwise would have.
What it all boils down to is, get used to this, but don't get complacent. This mod was balanced in part by a prideful handful of loyalists who think the content needs to be as punishing as possible, because the mod author wanted to make content that was tougher than usual. It's far from a perfect package, so while you should keep in mind that Calamity bosses are supposed to be pretty tough, there ARE bits here where it was way, way overdone. Like Devourer of Gods. Who was, at least a few updates ago, virtually impossible to beat without fighting in extremely specific ways.