This actually makes it more of an issue. If there is only 1 fight in an adventuring day and it takes 5-6 rounds to complete, the wizard has only 6 rounds to cast spells which mean they have only 6 chances to "get it right." Remember, a wizard cannot cast all their spells all at once. They take it turn-by-turn and if they're casting high-level spells, the amount of spells they can cast with an accurate guess dwindle in number and power.
Casting the 9th-level Wish for Forcecage only to have the creature pass a teleport save means that the Wizard can't attempt to True Polymorph in the encounter anymore.
And these series of guesses must continue, because actions are limited and truly strong spell slots aren't exactly the easiest to come by.