As a casual fan, I think Elvis has done pretty well tbh. If I was to be completely honest, I don't think his music has aged THAT well and I think he's better remembered as a cultural icon of America. Still extremely famous, if someone teen-aged and above didn't know his name I'd honestly be like ???
He was the king of kings salewise in the 1950s but then come the 1960s. He had been in the army for two years, got into gospel music, a horrendous film contract (courtesy of his money-hungry manager) and the world moved on for the most part as other artists took over. He had a bit of a comeback late 60s, early 70s but then that dipped again until he died in '77. Not sure how he did in the 80s/90s (probably pretty meh, his music hasn't aged too greatly), but he did have a revival in the early 2000s with the success of ELV1S and that amazing remix to A Little Less Conversation, I believe that was my first introduction to him and I was only a kid!
I feel if he wasn't thrown into the film contract (I blame Colonel Parker) and instead focused on his music career, trying to grow as an artist instead of rely on third-parties writers, he'd probably have been an even bigger artist.
When it comes to comparing him with Michael, I think statistically you can absolutely compare them, Elvis did
extremely well on the charts and even looking at "certified" sales alone rather than the claimed sales he does extremely well. Musically? Well they're both great singers; Michael's obviously better but Elvis had a great, iconic voice too and the songs he did suited him well. (I don't know how much he pushed his voice on his songs though?) and while Elvis has the upper hand when it comes to playing instruments, Michael
obliterates him in the songwriting aspect. I wish Elvis did write some stuff, it'd be interesting to see what he could do.
Elvis is a great musician, he wouldn't be the best selling solo artist if he wasn't... but musically... yeah. You know where I stand