I have no problem with them taking a wait and see approach at all those except backup QB.
They have young guys they need to find out more about, so getting the most reps possible IN and the preseason games is extremely important. They also drafted guys in the 1st and 5th rd (and 4th rd last yr) that they expected to take on some workload, its not like they did nothing. With PK they signed two young guys incl one of the op college kickers that was available, neither could do the job so they brought in the best veteran that they could find at the time. It remains to be seen if he is the answer for the season, or is even the kicker on opening night. He might not be. WR they signed a veteran guy who has played quite a bit and drafted another kid in the 3rd rd. Its not their fault the vet suffered a broken foot. WR is also a position that will likely see numerous people available at or after final cutdowns. There was no harm in waiting there, and they also knew all along Gallup would be returning fairly early in the season.
Backup QB is different to me because its clear Cooper Rush is mediocre at best and has no ability whatsoever to ever develop into a starter. Will Grier has some ability, but he is on his 2nd team now and wasnt able to practice a lot of camp. I di think they should have been fairly aggressive early in free agency getting a proven vet to be behind Prescott. Then, if Grier had shown enough maybe you consider cutting the other guy at that point, but not before.