You would be surprised how many games have comeback mechanics on them
The Guts System, the Gold burst and the Destroy on GG, Regaining Red Life on MvC2 and SG, the Heat gauge gradually increasing on BB, all the comeback mechanics on old KOF games, like i said, done right they are not bad, since they enrich the depth of the game by adding more strategy layers, perhaps your problem is that you see them as a reward (Don't use the crappy comeback mechanics of capcom as the base sample to judge all of them).
From what i remember the time is the same across all the characters, but the duration time was what it was changed.
Also Remember that the OD is still attached to the burst gauge, the strategical wight of deciding to burst or going for the OD will have a heavy impact on how often we would see them. Imagine that you are saving your Burst for an OD at low health, but you are caught in a combo that can kill you, you burst out of it and you wouldn't be able to go for the OD.