I think that there MIGHT, and I do mean MIGHT, have been a chance for Owen to ultimately have a legacy comparable to Bret's if a few things were different. The most obvious one, of course, being that he hadn't died so young & prematurely. The other is if he'd have been pushed heavily into the main event picture during the Attitude Era & beyond and wracked up several substantial WWE and/or World Heavyweight Championship runs. However, Owen Hart getting that sort of a push during the AE was a long shot and a Hail Mary to the extreme. Even if Owen did make it to the WWE or World Championships during the late 90s through the early 2000s, I think he'd possibly still have to contend with a mixed legacy because, frankly, championships as a whole have never meant less in the history of WWE than during the Attitude Era where titles frequently changed hands more than one time in a single month. Such frequent title changes never hurt the legacies of Austin, Rock, Taker or HBK but, let's face it, I don't think hardly anyone can realistically say that Owen was ever remotely on the same level when it comes to star power during that time frame.
Owen Hart was a guy with a lot of talent but, in my opinion, that talent has been pretty heavily exaggerated via nostalgia. When it came down to personality, presence, and/or charisma from the late 90s to now; Owen just wasn't in the same league with guys like Austin, Rock, Taker, HBK, Triple H, Orton, Cena, Punk, Batista, Bryan, Ziggler, Jericho, or Lesnar. I'm not trying to make it sound like that he didn't have charisma or personality but I never saw Owen Hart able to rally people for him or against him at anywhere on the same level as most or all of those I named.
From the beginning of Owen's exposure on the much bigger stage of WWE, he was still looked upon as Bret Hart's little brother. I think it became something of a double edged sword, a mixed blessing if you will. Owen's most memorable feud will probably always be against Bret as will most of his most memorable matches. Ultimately, however, Bret came out on top when it truly mattered the most. Had Owen come out as the winner of their feud, maybe he'd be looked upon differently and may have been elevated to a much higher level before his passing.
I think that had Owen Hart lived and he hadn't retired in the next 5 years or so, I believe he MIGHT have been somewhere similar to Chris Jericho. I think he could potentially have been someone who could fit in well in the tag, mid-card or upper mid-card pictures while seamlessly flowing into the main event title scene from time to time and getting some World Championship runs under his belt.