The K.O. for supers didn't really bother me at all, because they still serve the same purpose as a high percentage in SSB: it will K.O. your opponent.
In SSB, it was like:
Percentage Start: 0% >damage opponent> % up >damage opponent>%high > damage opponent > K.O.
No, it isn't that simple.
There are four phases in a SSB-Set (one Stock): "Build Up", "Dominance", "Endgame" and "Ledge-Game".
"Build Up" is simply the phase, where both player try to build up enough damage on the opponent until he gets into his "Danger Zone". This is the combo and risk heavy phase, because it is a save phase. since it is hard to KO each other. The player will use every move they have, but properly skip the strong but very slow smash attacks.
The "Dominance"-phase begins, if one player gets the other in the "Danger Zone" with his damage. This player dominates the other, since one good attack can KO the opponent. The dominated player will play much carefuller now, while the other still will take risk to land the finishing move. The problem for the dominating player is, that all his weak and middle strong moves are much less useful now. The player wants to KO the opponent and those moves rarely have the blast-power. This is a great balance and comeback point of the game. The dominated player has now much more options and can use the risky play of his opponent to catch up with him. The weak and middle strong moves of the dominating player even help him to get some space after those attacks.
"Endgame" is the classic point of all fighting-games. Both players are in the "Danger Zone" and will play very carefully. Since only strong attacks will give the player the KO, the game know also becomes much slower, but still great to watch. The longer the player stay at in this phase, the more damage they take. After a while the middle and weak attacks become useful again, since there blast power will also KO the opponent. A great gameplay-tool to end the conflict faster.
The "Ledge-Game" is the unique part of SSB, since the player get into it at any moment of the three other phase and it will end the set. It is the comeback, surprise, chance, danger and existing phase of the game. It is a highly risk and reward gameplay aspect of the game, which makes Smash Brothers so satisfying. If the player gets over the edge anything is possible. This phase is all about mind-gaming and skill, that's why SSB is such a great spectator-game.
In PBR, it's like:
Super Meter Start: Empty Bar >damage opponent > Bar fills > damage opponent > Super Ready (indicated by glowing outline around your character) > execute Super > K.O.
In my mind, the principal is still the same. The Super Meter is basically your opponents HP. You know that once that meter is ready, your opponent is going down, just like you know that once your opponents percentage is high in SSB, they are going down.
There is still strategy in the way PBR is set up. You are constantly observing the super meters of your opponents as much as your own. You are constantly looking for the best strategy to set up your opponent for a K.O, while avoiding be K.O'd yourself. When you see that glow surrounding your opponent, you start to feel that tension. At any moment, they could execute their super. When you see that they have a level 2 or 3, the tension gets really high, since you know there is a great chance of getting K.O'd/less of a chance at dodging/avoiding the super successfully.
The gameplay of PBR reminds a lot of the playstyle of Donkey Kong and Samus in SSB. Both have a chargeable attack: Donkey Punch and Charge-Beam. One major aspect of both is to get those attack fully charge and use them as an 100% KO move, if the player is in his "Danger Zone". It also becomes a mind-gaming tool, since player aspect you to use the move, if it is fully charge. I believe, it works similar in PBR with its super-moves.
The problem i see, is that missing the super-move means that you lose any progress you made in this set. If the player is really good in dodging those moves, you have no other chance to KO him. That could mean long and recurring "Build Up"-phases.