> Does all old "ATI" graphics chips need to run blobs?
No. I have an ancient radeon and I get a nasty slow 2D and the correct native resolution without any blobs.
I don't know if those cards you mention would work without the blob. Then there's also these probably worth looking at* https://trisquel.info/en/forum/making-radeon-work-again-bringing-back-linux-libre-34
* https://trisquel.info/en/forum/making-radeon-kernel-module-work-again
