The argument goes about it being unbalanced. If blobs are getting safer, more stable, and arguably more boring then pushing back that point with a soft limit would help things out. So would harder vassal/empire management and things like empires dissolving instead of lasting forever but that's a different story.
Again, if you really want to blob, you won't use holy war. What takes me several wars with holy war, takes a single subjugation/invasion. Holy war in theory gives you greater stability but you can just revoke all wrong religion vassals for free anyways and end up with the same scenario of right culture/religion vassals for stability.
Or invite claimant -> press claim