That's assuming that the area above will always be free of opponents, which is pretty wishful thinking. By your logic, I could say that players should always consistently grab the Time Slow in the map to surely prevent opponents from getting away, and yet the fact remains that they can fight back and even kill the Time Slow user.
Going down through the opening in front of Gravity Hold's platform is just one exit. As far as I'm concerned, one of the golden rules in deathmatch maps is to have more than one way out of an area, something which these stairs don't accomplish properly. You'd be surprised by how much these staircases get used even in Duel, and there's a good reason for that.
From a Deathmatch/Duel perspective, we have Gyro Attack, Water/Ice Wave and Power Stone, all of which you don't want to get close to and that can cover a lot of ground efficiently in the top area. We also get Crystal Eye, Napalm Bomb, Star Crash, Crash Bomb and Knight Crush, all of which can easily screw over a player bumping into the staircases.
You could also not strafe run down the stairs which avoids the ceilings altogether.
I was pretty sure I was running straight at normal speed and still bumping into them, but upon checking again, it turned out I was wrong. Even so, straferunning is a very common thing used in all modes (especially Duel where weapon placements are a thing), so I hope this suggestion is reconsidered. We've both pointed out possible outcomes of a match so far, but the most likely one in MM5DAR so far is bumping into those stair ceilings, and it most certainly isn't good when it does happen when trying to get away.