did he live up to his potential

Interesting quesiton...

He has had a long, very successful career (40+ years), so yeah he did great. However, he never made it as an A-list, though he definitely tried. More a B-level who can co-star in a big movie but is never the main reason someone goes to see a film.

Back in the mid-80s was his best shot, with DOA/Innerspace/Big Easty/Suspect, but it didn't work out nor last long. He never made it to Harrison Ford, Tom Cruise, and Kevin Costner status.

in terms of Coke, yeah.

Cocaine derailed him

He's overrated.

I think Dennis accomplished what he set out to do. He's a movie star. His marriage to Meg Ryan probably helped him stay relevant because at one point Meg was a bigger star than he was.

Yes. He's one of the lucky actors from the 80s class who continued to be a big star in the 90s and beyond.

Think of guys like Michael Biehn, Anthony Michael Hall and Andrew McCarthy. All good actors established in the 80s who weren't as lucky as Quaid.