A casual observance, but if Shaggy and Scooby beat the shit out of the monsters in anything but the Batman Brave in the Bold episode, it would send a terrible message to kids about solving problems with violence.
Anyway...Scrappy is a fun little foil to Scooby and Shaggy in the episodes where it's the standard SD formula of a guy in a mask plus one puppy because Shaggy and Scooby have to try to save him from being hurt. It shakes it up a little. At least in theory.
It's a little annoying in later seasons that he and Daphne take over Fred and Velma's roles of doing actual mystery solving and ghost trapping work, but at least those roles are there. 13 Ghosts is it's own thing but they have the same role there, and to be perfectly frank the skinny and fat ghosts were the worst characters ever.
Also it's own thing are the weird TV movies (Ghoul School, Boo Brothers, Reluctant Werewolf) where Scrappy is more of the straight man to the caper/situation at hand. Shaggy and Scooby get to be themselves in these and he's just part of the cast. The missing trio of Mystery Inc wouldn't fit as well into those plots so it's forgivable.
HOWEVER... The Scrappy Doo episodes that DON'T have dick to do with mystery solving, monster schooling, or ghost catching are atrociously bland and uncreative bullshit 11 minute shorts that have no mystery or caper at hand. Not to mention the bizarre shorts where he's with a DIFFERENT uncle/cowboy dog and his cowardly deputy buddy. They didn't even solve mysteries in that and the dude was a *cop*! That would have at least MADE SENSE. It's the worst of the HB fare that's bland and cheesy and lowest common denominator.
I imagine that if any kid actually loved Scooby Doo as a kid, they'd want an episode where there's at least a basic caper premise whether it's a mystery or something similar. A Scrappy episode comes on and you have a high chance it's NOT going to be the thing you like about the show and it's a waste of time.