WatcherCCG
Terrarian
Especially when it nerfs most powerful vanilla items to enforce its own "balance" and discourage their use in favor of its own content. (I fear for the new 1.4 weapons...)a mod that greatly overpowered vanilla wouldn't work well with it.
But balance disparity aside, Calamity does play nice with Thorium on a world-gen level. If the Bard and Healer gear had some means of scaling up beyond post-ML, then full compatibility might actually be possible. As it stands, if you want to run both at the same time, I suggest using Fargo's Mods to help bridge the gap.