After the last devlog I had the basic controls for scrolling and zooming a larger level. Mostly for a laugh, I threw in 1000 units and set up a huge battle. Tha...
Why do you have to update the positions so frequently at all? It's not an action game, shouldn't the units move based on pathfinding? With pathfinding you could only send the mouse click position to the server, calculated the path on the server and send it back to each player. It can then be played almost like an animation, that only gets interrupted through events like getting in range of enemy units or buildings, which could be handled like the projectiles with these network events, which, in addition, could send a full update for that unit.
Though I can see how your method is a more generalized, catch all approach and doesn't need specific planning for each new feature, though I guess we'll have to wait and see about that.
I also think that this scenario you are using to test is not very representative of actual gameplay if this will be a classical RTS.
With 1000 vs 1000 units I would guess that the pathfinding and especially collision avoidance between tanks, when they are actually controlled by a player, will be the much bigger performance challenge and will also cause a lot more delta updates which probably drastically reduces your current bandwidth savings.