While I understand that higher-end NHL players don't typically require a ton of time in the AHL, it is still a litmus test of sorts. If you struggle to be effective in the AHL, you will most likely struggle to be effective in the NHL. If you can't keep up with the pace and physicality of the AHL, chances are you won't be able to keep up with the pace and physicality of the NHL and need the AHL for more physical development time.
I don't, however, think you need to statistically dominate the AHL to earn a callup or that you can't be called up until you are ready to stick full time in the NHL. After you establish a certain level of proficiency at the level, you should be a call up option.
AHL players are absolutely awesome hockey players. The tip of the pyramid is just super, super small and they aren't at the top of it.