who else if not him
A reasonable question, but think about it, broham. There are tons of choices. Ronnie might have the very biggest (at least comparable in size to other 280 lbers., like Ruehl and Dillet. Matarrazzo had some crazy-big arms, too), but biggest doesn't necessarily mean best, even with the kind of mad detail and hardness Ronnie's arms had.
It really depends on the criteria you use. Would you say his arms were more complete than Paul Dillet's? Ronnie's triceps were thick, but consider how they looked in a side-triceps. When he was on top, they were cross-striated, but they didn't have the roundness or flair of Levrone's, Dillet's.
You could make a pretty good argument that Paul Demayo (don't laugh!) had some of the best-ever arm development. Biceps, triceps, giant forearms -- he had it all.
Then there are dudes like Freddy Ortiz, Lee Priest, Danny Padilla, Arnold of course, Terry Pastell, Sergio Oliva, Flex circa '92-'96, Vince Taylor, Brian Buchanan, that squinty-eyed Winklaar dude (at least for tris), Rick Valente for the same reason, Zack Khan, Victor Richards ...
I'm not saying any of the aforementioned necessarily have BETTER arms than Ronnie, but some of them do have things he lacked. Yeah, I know his forearms were huge, but no one in his right mind would suggest he had better upper to lower arm proportions than Priest or Oliva, for example.
Personally, I'd probably go with Dillet for best arms overall, but I have to admit this pic makes me straddle the fence:
Gunter's arms were HUGE there, yet Ronnie was making him look like a pale, smooth jerk-off. And I can only imagine Paul standing next to them; even in his prime, he'd be shaking and cramping up left and right, LOL.