Various spells being less effective is quite a big of a gap from the "invalidate" claim - after all, there might not always be a ledge and your barbarian might not be swinging them shortswords either. Sleep is arguable, because on one hand it's potentially less powerful, but on the other hand it's guaranteed effect now with set HP - you know exactly what you're getting - there is a lot of value in that in RNGfest that is D&D. They might further increase it though, which imo they could by adding another flat 6 hit points base and rank up, but that's what EA is for.
Same goes for many other spells that might be affected - they will either amend them, buff them or simply let them stay as is and the world won't end.
Okay, sure. But if you want to separate into situations where this overlap will or won't apply, then we also have to bring the word "invalidate" back into the argument. -In situations where you can get height advantage (probably most, given the encounters so far) faerie fire will be invalidated -In situations where you cannot get height advantage, but can still get backstab, faerie fire will be invalidated. -In situations where you can't get height or advantage, then faerie fire will apply as normal. Net effect: the effectiveness of faerie fire is lessened, just like I was saying. I was summing over these scenarios by saying, in general, these abilities are made less useful. Or, phrased another way, height (dis)advantage will sometimes invalidate these 56+ abilities, and sometimes not.
Also, that is a bold claim that Larian will fix these spells to be balanced. I haven't seen much evidence of that so far, or any indication that Larian realizes there is a problem. As you said earlier on this page, citation needed. And if they don't, then we as players have strictly lost options/tactical choices.