So in Shadowlands, warriors are getting spell reflect baseline. Makes sense, I think key class abilities like this should all be baseline. It's also getting nerfed to only reflect 1 spell though.
Why is this bad? Problem is there are so many passive effects in the game that count as 'spells' that use of this ability will be too tied to RNG. I only played TBC briefly, but when spell reflect was first in the game there were far fewer passive sources of damage counting as 'spells' (not that spell reflect was perfectly designed in the first place). This made it more skill-based to use, rather than getting wasted by, for example, someone's crucible of flame proc (or it's Shadowlands equivalent). Hell, druids are getting an ability that allows 16 casts in 4 seconds! How effective will the new spell reflect be against that? If for some reason they make the design decision to only cause it to proc from directly casted spells, it will need to be very robustly coded and you just know that with every new patch there will be procs and passives that break it.
I am someone who used to main arms warrior in PvP, as well as fought against them on my caster alts. The problem with spell reflect is that it lasts too long, with too short a cooldown. Often you only need it up for a fraction of a second, and the extra duration is unnecesary, but playing as a caster it's very tiring to face fury warriors YOLOing you and popping spell reflect to act like a divine shield while they go ham. What they should do instead is reduce the duration it is active for, as it is too strong in certain situations, acting as a mini bubble. Make it last for 2 seconds, even 1, on a 30 second cooldown, just don't make the spells it reflects finite. Making this choice (nerfing duration active and possibly increasing cooldown would increase the skill cap of the ability (and reduce its potency in certain matchups), but without making the ability RNG reliant, which is what the proposed change does.