You don't have to be married to a damage type for the feat to be useful. When a monster resists 80 percent of the spells you know, you'll be very glad you get to ignore resistance with at least one of them.Well yeah, I agree. I said it was a feat that could be helpful in certain conditions, if your campaign includes a-ton of monsters with one particular resistance and your character is for some reason married to one damage type (maybe a sorcerer with his small number of spells known). Other than that, it's way too situational.
Pretty much all demons resist fire AND cold AND lightning and are immune to poison. (TONS of monsters are immune to poison.) Yugoloths have all that, plus they are immune to acid. So you see how the list of damage types you have available is rapidly dwindling? If you aren't using Elemental Adept to bypass their resistances, you don't have a lot of spells left that can touch them. And if you haven't prepared the right ones ... well, I guess you can always fire up the utility spells and buffs.
All feats are situational to some degree. This one is far less situational that you might think, especially at higher levels.