now i guess a smaller pi zero can do this with a much smaller footprint

Pi Zero doesn't have an ethernet port, so you have the size of the pi+ethernet adapter then.

Technically, I believe Pi-Hole works over Wi-Fi as well: that is, you can have the Pi Zero running Pi-Hole connect to your router via Wi-Fi. Then all your devices connect to the Pi Zero for their internet access.

I could be mistaken though; only over installed on a Pi 3.

You're right. I have a Pi Zero W which runs Pi-Hole over wifi. My mobile devices use it as a DNS server.

I've been playing around with orangepi zero for when I just need ethernet, wifi, and USB. It fits in an Altoids tin with room for some cable management.