Neural nets and machine learning in general are good for problems whose solutions are hard to hand-code. If you can hand-craft a solution there's no real need for machine learning and it might simply take up resources you need more elsewhere.
This is actually something I see as complementary, so the AI on the server has to decide the general direction and then on the client these flocking simulations can be applied for scale if you have the processing power.
I'm thinking each group of mobs has a server directed leader, who's position is server deterministic and then to save bandwidth the PvE minions and their movements can be generated on each client, just tracking when they are killed.
I'm not scared of desyncing in the details. As long as the PvP stuff is coherent.
https://www.oreilly.com/library/view/ai-for-game/0596005555/...
Neural nets and machine learning in general are good for problems whose solutions are hard to hand-code. If you can hand-craft a solution there's no real need for machine learning and it might simply take up resources you need more elsewhere.