But, then we slam into the "wall of DM" where the DM, in thinking that he wants a certain type of game, then sets the DC based on his or her "feelings". And those feelings are almost always wrong. That's the problem.
There's an additional wrinkle that's specific to 5e, I suppose, and that's the replacement of numerical modifiers with advantage or disadvantage. Since that's the default bonus/penalty, I could see it further restricting cool maneuver attempts.
Example: My lightweight fighter is up against a bruiser. Cinematically, the hero in this circumstance typically tries to outmaneuver the foe, using his greater agility, etc. Buying into this, I want to try a classic move, wherein my character somersaults over the foe to then strike at his back.
It's the middle of combat, so having a long discussion about the different ways to interpret this is gauche; the DM needs to come up with a ruling. She assigns a DC to an Acrobatics (or should it be Athletics...) and if the player pulls it off, they get a bonus, which in the 5e game defaults to Advantage.
As soon as the fighter hits 5th level, this maneuver (even with a reasonable DC) is not worth it, unless the DM allows the full compliment of attacks after the somersault (which I have not seen, and I've seen the maneuver attempted more than a few times). The penalty for failing the Acrobatics check would be...advantage on attacks against you? The Advantage/Disadvantage mechanic, streamlined as it is, lends itself to boxing in a bit more than at first blush. Maybe that's a fair trade for not tracking modifiers, though.