Mary was nowhere near R Kelly in terms of competition. Dude wrote, sang, arranged and produced and then gave legit hits to other artists on Michael Jackson’s level. shyt, he even blessed Mary with some piff.
Mary was a raw muse that Puff basically made in to a female solo Jodeci and then did the same shyt with Total. Mary came around at the right time in a post-New Jack era and instead of taking a Whitney or Toni Braxton lane, she was given Hip Hop flavored tracks to sing over along with seeming less polished like a typical soul/R&B singer. She sold that image well because it didn’t seem manufactured.
Behind the scenes you had Puff’s whole team cooking up songs and leaning heavily on samples to drive it home (the My Life album especially)
R Kelly was already on his way to being a golden boy in the game by 1993 and by the late 90s dude had a crazy discography as a singer and producer.
And this is if we are strictly talking about talent and abilities. He has her beat vocally, as a producer/writer/arranger (she cant do any of that) and he could oversee someone else’s project and that shyt will actually turn out well (Aaliyah’s first album, Isley’s 90’s comeback album)