useless has the most confidence

Shaggy is Ranger and Scooby is the Druid

I only choose these because Scooby has been shown to shake off frightened status effects, and Shaggy has been rumored to have an affinity for plants.

Jinkies!

I would say Velma is closer to an artificer, but that's just my opinion.

Fred was the one who built the traps, so that might fit with him. I just saw a pic of all of them with her leaning over a large book and thought 'wizard'.

Ah yes "plants"

Ah that makes sense. The only spell caster I've played is paladin, and i mostly just hit stuff or intimidate everything.

My group considers the paladin's entire job to either prevent the evil and neutral players from doing bad things to the villain, or get tricked into doing bad things to innocent NPCs.

At some point, Daphne learned martial arts (I believe when Sarah Michelle Gellar starred as Daphne Blake in the 'Scooby-Doo' and 'Scooby-Doo 2' films then the producers for future reboots at and beyond 2002, starting with 'What's New, Scooby-Doo?', went with it), so monk would be better suited for her.

Bard could be moved to Scooby or Shaggy. If Shaggy, Scooby could be the druid since it's already mysterious enough that he's a talking animal, and bards get themselves into weird shenanigans as well as far as Shaggy's goes.

Everything else looks spot on—especially Scrappy's.

I did not take multi-classing into account. Or the fact that different generations of fans would view the evolving continuity of each member of Mysteries Inc as different classes.

I didn't suggest any multiclassing—honestly not really sure who would multiclass into what yet since my memory's a bit hazy about all the Scooby-Doos I watched, and whichever edition or reboot of Scooby-Doo your post is based on wasn't specified so I just went with what I could remember of each canon fact about the gang up to this point in time.