I play a wizard (currently 9th level) in tabletop D&D 5e and without Concentration to limit her, she'd be almost unstoppable. Concentration is a game-balance mechanism. It might not seem to be at lower levels, but when you get more spell casting slots and access to more spells it becomes important.
Since D&D was around casters always started pretty weak and got stronger later on, read some novels on Elmister, Khelben, Gromph, Mordenkainen, to list just a few. Rulewise you can still stop them. The other classes get better at mitigating the effects of spells too. With spells like "wish" in the pool such things are to be expected.
I do not say that i do not understand the logic or even the plan on the concentration mechanic. On some spells i think it fits pretty well. But compare "hold" and "sleep":
As of now you PUT people to sleep but have to concentrate to KEEP them paralyzed. OK. Works.
But could you not also say you paralyze people for a TIME (as has been) but you need to concentrate on the sleep spell to KEEP them sleeping (mostly during a very loud combat situation which would wake up even a drunken dwarf). Against both spells victims get a save but against hold there are much more ways to break it.
In case of hold, maybe give an extra save each time the victim takes damage.
Another way would be to rename concentration to a "maintain" mechanic. Give casters a certain amount of spells they can maintain, getting more by level and add situtations that require a concentration check while maintaining. In case of hold a concentration check when the victim takes damage. Something along those lines.
Or, like mentioned above, a damage threshold before a concentration check is necessary. Either depending on HP or CON. Like half of constitution + modifier (like a profiency). That way even a CON 8 caster would need to take 4HP damage to have his concentration broken. That would remove a lot of things like acid or burning from a certain check each round.
For falling prone, just add +5 :P
