I think that at this level, with the amount of money spent to get to these finals, being legitimately 100% sound should be the baseline. Like it is for dressage, FEI eventing and FEI showjumping. There is no excuse to ride a horse at this level and height who is obviously sore (or head-bobbing lame). And they should in no way have put a horse that was obviously not sound into the top 5 to test.
Serviceably sound has it’s place, but competing at the Maclay Finals is not it.
Edited to add - mechanical gait abnormalities like stringhalt are obviously excluded from the above.