I personally wish that some mechanics could be disabled from DLC. For example the Religious League when Reformed faith dominates the HRE. Buddhist religion changes in Common Sense.
I sort of agree, but this is a better sign these mechanics aren't working too well. If we're seeing reformed painting 2/3 of the HRE and 5 protestant minors, the current league war setup is nonsense. Under such a scenario we have no historical precedent but would anticipate the "reformed" religions carrying weight and posturing in the HRE more effectively. Creating nonsense outcomes like "Catholic league wins" but having 3 eligible Catholic nations left suggests that the mechanic needs work.
It's the same deal with Buddhism. The over-arching mechanics and incentives in the game make the karma slider as-implemented an active detriment to the faith. If something is going to see development time and marketing as a fun-to-use feature, strong disincentive to using it at all because it gets in the way of basic gameplay is questionable. Then again, pdox seems pretty hard-set in making the Abrahamic faiths far and away the best, so I doubt we'll see it turn good, maybe viable if we're lucky (Hindu is viable at least).
It causes lots of weird bugs depending on which expansions are flipped on and off, and it's not worth having those bugs there for the sake of that tiny percent of achievement hunters
This still doesn't make sense. Aside from achievement hunters, who would encounter said bugs, and who among this also-rare subgroup would be advantaged by being unable to continue the save whatsoever without identical DLC they may or may not possess? It sounds more like an "incompatible versions" thing to me.
And I'm saying this as someone who has never tried it personally. It just seems odd.