Popcap and map sizes are unchanged since AOE2: The Forgotten, though, and the other items are not in the deterministic simulation.

AOE2 HD wasn't multithreaded, so we should still have an order of magnitude more CPU performance at our disposal these days.

The pathfinding has been reworked, yeah. It shouldn't have made the game 10x slower.

In any case, if it already supports 8 player with 500 pop, 16 with 250 is not really any different.