Spring build-up is pollen-limited, certainly here. Thus if there is ample opportunity to get out and good warm weather, colonies get ample pollen and raise good quantities of brood, but if the weather is cool or wet their brood raising is limited or halted. We had exactly this at some sites in 2021 (the most recent bad EFB year... long periods of stressful spring confinement).
It's the protein content (mostly) that's needed for brood food. We're not feeding patties to avert starvation (syrup or fondant would be more appropriate) but to support brood raising. Each cell of pollen you see around a patch of brood is enough to feed two larvae, so the turn-over of that inch-thick ring of pollen is rapid.
Occasionally we have a proper June gap and apply patties, especially to May nucs. Of course it varies from apiary to apiary.
We keep a stock of UltraBee patties for periods of poor weather - bees take this down readily and will continue / restart brood raising on it. We've tried others before and I recall in particular that FeedBee was dire - either mixed or as patties - they wouldn't even touch it to shift it out of the hive.