I've seen battle cinematics with loooots of units on screen and I've never seen those "spikes" in-game*, only some lag.

Could be dependent on your hardware though, but I remember back when warcraft 3 was still new and your PC is probably not 15-20 years old.
Have you tried testing without the doodads ? Select them all, delete, save & test the map and then just undo to avoid losing your work.
* well once or twice with some custom models glitching, nothing to do with the number of stuff on screen