From what I read we won't need it because all the Pokemon can be caught on either version and since they aren't compatible with prior games we don't need the GTS. The sequel to this game will need GTS, but not this one.
Now, if you just don't want to have to deal with trying and succeeding in catching them all and the GTS was your way out, I can understand your frustrations. Personally I've never cared about catching them all, I just go after the ones I want to use and ignore the rest. Well that was until Let's Go because you could level up by catching haha.
But you still need someone else to trade, and that will be an issue.
What about gengar, machamp, rhyperior, accelgor, excavalier...? All of those pokemon evolve through trade, if you don't have anyone to trade with, you won't be able to get them. The GTS was the perfect answer for this, and it's gone now...