James Gunn turbo-fucked the IP by introducing meta humor and LGBT Velma into this franchise.
I agre with a lot of what you wrote, but you can't place meta-humor at James Gunn's feet. That was present as far back as 1985's
A Pup Named Scooby Doo, the show I personally see as the real starting point of the rot.
For me, the ultimate problem is...
Okay, Scooby Doo from the 1960s to the start of the 1980s had a good balance of comedy and horror/mystery (even if in a safe-for-kids/Goosebumps sense). Like look at some of the location shots and backgrounds from the 1969 show... they could be legitimately spooky, and I remember this being something that stuck in my head and kept giving the show a certain allure and air of intrigue when I was a kid. Hell some of the actual monster designs themselves are kinda creepy. The
thing from A Night of Fright is No Delight for example.
Weirdly enough the more serious horror/mystery aspects seem to be something the older seasons leaned into. But then
Pup came out and suddenly people got it in their heads Scooby was meant to be comedy.
Zombie Island almost reversed course but unfortunately....
Also, around the 1980s/1990s was when writers began thinking that Fred, Velma, and Daphne having basic personalities was somehow a
bad thing, and thus decided they needed "fleshing out." Which is fine, in theory.... the problem is nobody really had good ideas about what to do with them outside of playing to their already-inferred archetypes. Which actually flattened them rather than fleshing them out.
Like, in the 1960s show you could accept that Fred, Velma, and Daphne were basic teenagers who had mild differences but still got along and had enough in common. They didn't stand out but they were cool, guys you could have a few drinks with.
By
Mystery Incorporated (and why is it that its always the highly-regarded elements that I tend to have big issues with?) we had Daphne being
such a snob that touching fake leather gives her hives. Yes they literally do this in an episode. And Fred reads a magazine called "Traps Illustrated."
It's almost a Scott Cawthon thing with how there's a distinction between "what a normal person would think" and "what someone heavily involved with this franchise would think."
NORMAL PERSON: Fred makes traps because these crooks are legitimately dangerous and he wants to capture them with minimal risk to himself and his friends.
SCOOBY WRITER: Fred makes traps because he has some bizarre fetish for making traps even when he doesn't need to.
Ironically Shaggy and Scooby legit had more depth in the original 1960s show. They were cowards but they were wily cowards and if their brain saw an opportunity, they would take it. Scooby legit
beat up an ape-man...
and won.
But I almost don't want to mention that, because you know where
that would go if modern writers got their hands on it--suddenly Scooby would be this badass martial artist who never gets scared at all. Which would be just as bad as modern writing where Scooby and Shaggy are often just given any personality trait the plot requires.
It's actually amazing how many opportunities they miss. Like in the Wrestlemania one, they make Shag and Scoob wrestling fans--which further hurts Fred, Velma, and Daphne as they basically never get this sort of personality expansion, while at the same time making the main two feel like blank slates you can graft just anything onto.
Like, here's an idea: What if
Velma had been a wrestling fan instead of her whole "too smart for this" shtick? A lot of wrestling fans
are nerds, after all. Or like, how about just remember the times Shaggy mentioned that he was on his school's track team or had other athletic accomplishments? How about remember that whole period where Daphne was actually a good detective? How about
anything but what WB is doing now?
Legit sometimes I feel like I could make my own Scooby series... but it would just get DMCA'd so why bother.
Also I totally agree that Scrappy hate is old. Honestly I didn't even dislike Scrappy and I think Scrappy hate is one of those things that was astroturfed by the internet. But in general its just retarded to ever say "the fans hate him? Well so do the characters in the show!" Full stop, the characters are not stand-ins for the fans.