It usually is, but that depends on the additives used and the gram strength of the flakes used to cook the glue and the quality of the glue job.

E.g. I cooked a batch of 192 gram strength glue with 50% table salt additive to keep it liquid at room temperature, and I had half of the failures at glue seams in destructive testing. Made an excellent glue for cold winter days, though.

In glue strength tests (like James Wright on YouTube and FWW magazine both), hide glue compares favorably to modern glues.

But all it takes is a few drops of additives to drastically change the qualities of the glue.