Keep in mind that FPS drops are only one issue with Denuvo's performance. Another common one (which i think is more common in recent releases, judging from comments i've seen) is frame pracing/stuttering/etc - people very often mention in Reddit threads about Denuvo's removal from a game that the update that removed Denuvo fixed these for them (of course it could also be some other change the game had, but this has been the case with more than one game and games receive other patches before removing Denuvo, so i have a hard time accepting all are coincidences).
A slow/lengthy call every few seconds wont affect your average framerate (which is what often developers check for performance measurement) but it will affect your frame pacing and give a stuttery feel. Most people tend to call this a "performance issue" (regardless if it is due to performance or not).