I think Hollywood did a great job of selling Ahnold to us through so many profitable years. I admit I've been somewhat of a fan too - "somewhat" being the operative word - but I think (to think of a parallel) The Rock has been a better actor than him. It's now more evident after not seeing Ahnold in a new flick for some time. I was watching parts of "Total Recall" the other day and I realized how bad his acting actually was.
I think Momoa will be a better actor than him and a better fit as Conan.