At other airports, the FIDS manages a 'go to gate' alert, why not for the satellites at T5? More pertinently, why is it not possble to know the gate at -3 hours? Unstable stand planning seems a likey culprit, which is unbelievable in a purpose built new terminal. They can allocate stands at -24 in AMS.
I think the reality here is that at AMS I have never seen a full terminal with no free stands. There are always free stands when busy. Due to our British lack of foresight, I know that Terminal 3 at LHR is occasionally actually full, ie no more room. Inbound aircraft are advised on approach by handling that "no stand allocated as yet" due to the fact that they may be waiting on a flight to clear from the gate they are supposed to be on but it's going to be either a gate change or a ground hold. LHR has less space for the flights it has and so stand planning is that much more dynamic.
Bit like hot bedding in the NHS, they had enough bother getting permission to build T5 the size it is and it was known even then it wasn't big enough. I have seen T5 airbridge stands maxed out and even pressure on remote parking. That's why it struggles the way it does.
F3G in many ways, modern Britain is regressing alas.