Two issues:

Luna can detect group size, but is missing a 25-man comp (I doubt 20 is much relevant in TBC as well). When a raid goes above 20 members it goes to the 40-man comp profile.

Secondly, the auto profile swap is extremely slow; takes a proper 10 seconds to swap profiles which is very dangerous if a raid member joins or leaves during combat. Is this even something that can be improved?

The profiles do not swap during combat. They swap the next time the player leaves combat. And yes, i do not know how to improve load times as basically everything gets reloaded.