It's not about how big they are, how many wins they get, how many clean wins they get, etc, it's about how often you job them. That defines a heel.
Edge/Jericho for instance, neither were "big" men. Neither were "badass". What got them over was the fact that they worked characters, and they weren't JOBBING 3 times a month.
This is the single biggest issue with WWE programming, and it's why heels and faces both struggle to get over or stay over.
You say Seth Rollins is the new "top heel"??? Well, he's already jobbed to Cena, Ziggler, and Reigns, all on weekly shows. That's why he already looks inferior to basically every top guy on the show. He can win as many matches he wants, it doesn't matter. He's already LOSING as much as he wins.
Rusev isn't over and credible as a heel because of all of his wins, it's because he hasn't lost. And when he eventually does lose, he can STILL be a very over and credible heel. As long as you give him a loss and then protect him. But the way WWE books is, he'll lose a match and then he'll job for three months straight on weekly TV. Then they say "Why isn't Rusev a beast anymore?" well that's because you fucking ruined him. It's not because Rusev didn't want to be a top guy, or doesn't go for it, it's because you have no fucking clue how to book.
Look at Ryback's first "push" where he "turns" on Cena (despite the massive face pops he got for it), then proceeds to not win against Cena for three months. Then starts jobbing on RAW. Then starts jobbing on SD. Then starts jobbing on Main Event and Superstars. How come Ryback isn't over as a heel, despite having a godlike physique and being strong and badass? Oh, because he does nothing but lose.
If your identity as a performer is to lose left and right, you're a failure. Unless of course, you are a jobber, mid carder, low carder, whatever. There's nothing wrong with being that, everyone has their role to play in wrestling.
Heels are so easy to build. All you have to do is making beating them matter, and WWE doesn't do that. You can be a "chickenshit heel" and still make for a perfectly good match up for the faces. All you have to do is not-lose every single week. But WWE's "Guy A vs. Guy B" philosophy has ruined this booking method.
This is why Cena is bad for the top of the card. Cena/Punk ruled because it was handled like a true old school feud. The guys interacted, cut promos, never actually wrestled or touched each other on weekly TV, there were no random tag matches with them, they treated it like a money feud. And it felt like a big deal because of that. But it is literally the only instance of this type of feud-building in the last five-ten years between active performers. You just fucking watched it with Rollins/Cena. They have a PPV match and that's not good enough, they then have to face each other two more times on live TV in the next month, with Cena winning the blow off match. So in less than 6 months as a main eventer, we've already confirmed that Seth Rollins is not good enough to beat John Cena.