Everything has a huge opportunity cost. You’re giving up alternatives for every choice you make. Lowering variance of high impact attacks has value if you choose to play that way. Missing can turn a battle.
It doesn’t have to be useful to every choice of every build to have its existence justified. There are plenty of choices of spells, equipment, etc that I can look at and tell you “I’ll play 20 different times 20 different ways and never be tempted to use that once”. That’s perfectly fine.
I’m not saying “True Strike shouldn’t exist”. I’m saying as it is, it’s incredibly underbalanced and not worth spending two turns to cast one spell.
I’m all for build diversity, but if you want to guarantee your big spells land (you can still miss with advantage, btw) you might as well pick Divination Wizard and use a Portent. If someone wanted to use this cantrip and I was DMing, I’d adjust it to be more accessible.