IMO, yes.
Half the fun of waiting for a KH game is speculating and subsequently seeing what ff characters will show up later. Knowing that there's really no guarantee that this element will be represented and, in this case, straight up dropped whenever they want has been incredibly disheartening and has, honestly, soured me quite a bit on the series going forward.
I could see a solid argument for removing them if we got something better by their exclusion, but we didn't. The worlds are just as superfluous as before except now there's no buffer for the Disney stuff.
The removal of the FF stuff just highlights even further how big of a waste of potential Kingdom Hearts is because the Disney properties aren't allowed to interact at all (and in cases like Frozen or Tangled, even the KH cast isn't allowed to interact outside of stock replacements for previous elements from the source). The idea that there'd be no room for them mixed in with Disney's strict corporate sensibilities extremely limits what Kingdom hearts could actually be, as the actual possibilities for what stories you could tell if Nomura was capable of/allowed to mix up different Disney and FF properties together is immense.
Like, using Olympus as an example, imagine if Hades was fighting against a new 'God of Death' in the form of a new arrival, Lightning (based around her Lightning Returns persona as a sort of Reaper Goddess) or him enlisting Lightning as a replacement/upgrade to what he tried to use Cloud for in KH1 and dealing with the concept of life and death or the subjugation of souls, both in reference to Lightning being controlled by Bunivhelze/Hades and mixing in with the concept of a Soul, since KH deals with those themes. Or, as another example, mixing in Zidane or, appropriately, Vivi when dealing with the concept for replicas, another vital component to KH's story. Based just on the stories we got in 3, they could've fit them into BH6 or Toybox fairly easily.
TL;DR The removal of FF elements makes the series feel less charming to me as the reason for their removal comes across as a mix of laziness and corporate stinginess.