RE: "checking against every CT entry":
You may have solved this already with 5e Legendary Assistant, but I just want to mention... with Combat Groups, maybe there is a way to calculate only on what is visible in the CT.
I know that doesn't help every situation, but if there is a way to avoid a bunch of needless calculations, that might be excellent.
I'm not sure if Legendary Assistant does look at all (including hidden) CT entries but just doesn't report notifications on them (with the option toggled off), or just doesn't look at them at all somehow. If it is the latter, there might be some other extensions out that that could benefit from that methodology (Clock Adjuster comes to mind).
Thanks for all you do!

