The guys from Limbic simply don't know how to make games of this caliber and in this genre; their fault here is perhaps that they agreed to undertake such a project for Ubisoft and on Ubisoft's terms (with a low budget). However, if they had refused, Ubisoft would have hired even lower-budget developers (and, moreover, without experience working on the 6th installment), and the situation would have been even more dire.
Bugs and synchronization issues are only a superficial reason for the failure. Saving on the technical part of the game could not but affect the saving on gameplay and game balance. And if some players are weeded out due to bugs, others are due to the gameplay. For example, I didn't see any interesting battles or interesting units in the game. This does not mean that they are not there; it's just that, from my point of view, the combat and units are not well-developed enough. And looking at the city structures, carefully preserved from the 5th installment, it became clear that the game is not very focused on Multiplayer (too slow development). And there were also statements that esports is not a priority (what is esports? It's high requirements for balance, multiplayer, and dynamics).