Concentration-gating. What do you think?

[Ady]

Drawing on an abundance of experience with Concentration, the initial feature of the system that was pointed out: that you have to compare between spells, it actually far more of a hassle than anything for designing spells. The 5e Druid and Warlock are hit the most by this, as a majority of their spells are concentration, which means they end up casting one spell in a fight and holding onto it for as long as possible, spending future turns on meager cantrips, which is intensely uninspiring, and forcing all future releases to creep up the power of concentration spells or just see them go unused.

It's also somewhat infuriating in the case of clerics, where Bless is certainly one of the best spells to keep up at all levels due to the complete lack of spells that provide non-advantage bonuses, and yet it's a spell they get at first level. It's hard to say there's a lot of tactical consideration when the best course of action for a cleric is immediately available and hardly changes.

I personally prefer the system pathfinder, and more specifically spheres, uses. Concentration can be removed by spending points on it usually, and there are ways to make concentration easier (Easy Focus) or give the concentration to others to maintain (various Teamwork, Mana sphere, Familiar and Companion feats). All Backporting does is make it less taxing to keep a single spell up, but significantly limit the overall amount of abilities you could use.