Arnold is politically vacuous and was a non-entity as a governor. Someone who sought power for fame's sake and when he got it realized he had no idea what to do with it. He did nothing for 8 years, rarely even tried to do anything, and he has no policy stances of note on any issue ever. If he's in the presidential conversation it's because people are impressed by optics and people saying canned lines and the fact that the guy "acts" in 9-figure budget CG shitfests. "I'LL TERMINATE CONGRESS!!!!"
I'm not a Republican (or someone legally allowed to vote in the US)--but there are Republicans in the field who are manifestly unqualified regardless of their policy stances, and then there are Republicans who are basically qualified (but arguably wrong on the issues). Like, I don't think Scott Walker would make a good president, and I disagree with a lot of what he's done on Wisconsin. I wouldn't give him a high rating. But he's not someone whose mere presence in the conversation makes a mockery of the election process. Whereas a Donald Trump or Arnold is, imho.