He was very good, but fell short of great. And of course he could COMPETE today. Stevie could compete in any lightweight era, and if he was around today he'd be by far the best opponent of Loma's career.
Johnson was an excellent fighter. As for competing today that's kind of funny to me. Besides the extremely talented Loma theres no one Johnson couldn't beat. This era doesn't produce better fighters than Johnsons. I'm wondering why you ask that?