The CDL allows one or all of them to be missing with various penalties
Clearly
(a) I stand surprised
(b) AI saw a commercial advantage for the CDL entry.
No performance problem operating without them with stall-related penalties. The concern relates more to what happens at stall ... one presumes that the stall characteristics of the A320/1, with asymmetric chines, are relatively benign ?
Flying a 321 with one missing isn't that unusual if a 320 cowling has been fitted as a temporary measure
I don't think one would expect to see any noticeable (to the pilot) difference regardless of what was missing ... other than in the stall regime.
A quick looksee through the FAA MMEL doesn't immediately show an equivalent MMEL provision. What does AI term the devices ?
As a consideration, I am aware that some of the light twin VG mods (which have the same intent to control stall speed) can demonstrate "interesting" roll character at the stall ...