This is spot-on for the theme--I think this sort of thing is exactly what Willem was angling for. Tower defense has always occupied a funny space of almost-but-not-quite taking off, and you make a nice compelling case about how you could expand it into a deeper experience that would encourage repeat play. I like that the player is both attacker and defender simultaneously and that you have to choose and customize both types of units. Between team play, AI bosses, quests, seasonal events, and everything, you're really describing a rich and rewarding experience here. I would play it for sure.
My main comment is just on the GDD itself; I think you hewed too closely to the template and could have just cut big sections that aren't relevant to your game, like the entire Plot section. I could also have done without the Midjourney pictures, especially since they don't fit your written description very well. But hey, if the worst criticism I have is your document formatting, you're doing well.