Yeah losing crit, det, or dh from materia melds is one thing, but speed is problematic for the integrity of loopium and a lot of rotations.

For ultimates it's an actual problem for the old ones that don't use modern gear anymore with materia, but just live on synced down gear where all substats are filled anyway, but you can always work around it by using other gear. Generally you prep for them before. It's more of a problem for synced random past content, even though it's not like, a huge bother for more casual content, but it can be mildly annoying.