Then tell us how you are going to attract to the game and monetize FTP RTS? The FTP model is not suitable for the strategy. The FTP model implies that for the donation you accelerate your progress. What is the progress in RTS with the base? You can count anything, but the FTP model may not attract to the game, but destroy the mechanics and gameplay. After all, all this must be reworked for the sake of monetization.
CoH 2 literally already had the trappings of a successful Free-To-Play model. Literally just the exact same except you allow players to spend money for Supply or buy commanders/skins directly. And then balance the game so that it's not Pay-To-Win (i.e. you can still win with default units). Add lootcrates with rare skins, add skins for the camo on your units, knife skins. It's too easy.
It's a tall order for sure, though.
EDIT: Actually you DON'T allow players to buy commanders and skins directly. Make it so that if you buy 5 dollars worth of supply, you can buy X amount of commanders but *just* a little bit lacking to buy another. That's another dirty secret of free to play models.