Hello!
My suggestion has to do with Battle Effects Settings under Character Configuration specifically in PvP. Currently there are three options for Own, Party, Others, and PvP Opponents which includes Show All, Show Limited/Some, and Show None.
Currently, not all Limit Breaks appear visually if Show Limited/Some is selected. For example, if you have "Some" selected for PvP Opponents, reactable Limit Breaks like a MCH's Marksman's Spite crosshairs or a WHM's Afflatus Purgation laser beam, you won't be able to see the spell animations making them difficult to react to/Guard.
So, my suggestion would be to make all Limit Break spell animations visible when Show Limited/Some is selected OR add another Battle Effects Settings option specifically for Limit Breaks in PvP so players who want to be able to see all LBs but not all spell effects can have that option.
Anyway, that's pretty much it. Thanks!