If there's one thing that the new shitty Disney Spider-Man show did, it was how easily it is to make Gargan a threat. Just have him be a strength spec Spider-Man.

Or hell, if he doesn't fit in the current landscape of Spidey villains, run with that. Make him an outsider to the villains. I don't care how. Make him a vigilante to run with him being JJJ's "Better Spider-Man" but still being...well, Gargan. or Hell, bring back Superior Spider-Man and have Gargan having to be "Better than Superior".
Run with the fact that he's more of a mechanic with his tail than Spider-Man is an engineer with his suits and shooters.

Scorpion's plenty easy to get back up and running, you just need to do stuff with him.
A new mask would be a good start.