I use DP alt mode and also the HDMI port to drive two screens. I use hyprland and runs fine after configuration.
My battery certainly last a few hours. I use it as any other laptop I had before and use it daily on trains. So I cannot at all agree with your POV that it's a desktop. The battery is working without problems.
Do you actually use dp alt mode and not HDMI for external displays? What DE/WM are you using your mac with?