When I first saw Scooby Doo, (Where Are You? the original show, watched from the beginning), the demasking reveal trope was fresh and new. What many don't realize it that Scooby Doo had been intended for primetime and been cast to Saturday mornings during a slow purge of animation from primetime, where it was far from idiotic.
You may well have seen later seasons after the storylines began to be dumbed down. Remember, Scrappy Doo was a stupid idea, adding comic relief to a show that already had it, and worse, then dumping the serious leads and giving their role to the original comic relief so that Scrappy could scream "Puppy Power!" and offend all the older fans.