DY: We could argue on M’tzius all day. I do not deny that there are people who do as you say (though it’s probably combined with a belief that Sefardi Havara is more legitimate), but I don’t know if they’re the majority in the “Modern Orthodox” community.
The P’sak doesn’t make sense to me either, but I’m pretty sure it’s in the Yabia Omer. It was well-known that R’ Ovadia thought that all Ashkenazim should switch to being S’fardim anyway, so I’m not sure why it would be surprising.