I am a professional by the way. I made a hex-grid rts with player controlled unit pathing.
Also, i don’t see the problem with networking thousands of positions, that sounds normal. It is up to you to decide an appropriate frequency to send them.
So, if you have thousands of units, id assume their positions are getting networked at some frequency already, right? Then you don’t even need to network the paths.
Alternately, if its your paths that have the thousands of positions, well you need better path encoding that has fewer (ie, north 5, east 1, north 25). Also, like i said before share paths between units, and only send the path once or when it changes.
Re: it sounds to me like maybe the overall path from spawn point to the destination is not changing much, its only sections along it where a player may have built something, which needs to be passed through. So, for that section, have it network for each tile, how close it is in steps (considering obstacles) to being past the section. This would be recomputed when obstacles change.