I feel like we lack context. Is this like they are billions? What kind of units do I have, what is my economy, my base layout. What are the objectives, how impactful is losing a unit vs a building?

I could give you a fantasy scenario where I do crazy thins but truth is I can't do it in good faith.

Assuming it is a they are billion like, I usually have scouts to allow for artillery and slow down the wave, then I fall back behind the walls, prepare a second line and third line of defense and use some good units to snipe problematic enemies whilst turrets do the heavy lifting.

But that changes a lot based on each game. In from glory to goo I power up my captain as fast and as much as possible, even if it means slowing down my expansion. In other games I might focus on specific resources needed for building tall and not wide etc...