I've been restoring the floor with 2 Master Builders and 1 Adept Builder for the past hour and it's STILL on 1 percent! Is it supposed to be this slow??

No! It didn't take me any longer on the floor than it did on the vines by the gong.
Maybe your game is on a slower speed. That might have something to do with it.
I had my game on 2X the first time I played.

I also felt like it was the slowest building project.

what speed are you playing on? that could affect it also.

My builders were somehow reluctant to stay and work on the ancient floor. They did a couple of turns and then went away and did something else, like fixing huts or admiring something, before returning. It's similar to the hidden gold chest in VV1 - they were equally slow and unwilling in that project. The other projects were much more interesting, as it seemed. The game speed didn't matter; the behaviour was the same.

I had about 3 working on the floor and I still had others clear the vines and and then build the hospital before it was done. It's about 78% now. And I am running at 2X!

its been very slow for me 2 even on 2x

I kept trying to inspire my villagers about the ancient floor - reminding them of how they'd collected pebbles here, been curious about it throughout their childhoods. Generations before them could only look upon it with curiosity, and now they had the privilege of uncovering it. Show a little enthusiasm why don't you? But no, they took forever to complete the task.

It does seem to take forever, I agree. The presence of the stream nearby seems an irresistible temptation; the builders seem to keep wandering off to cool their toes or take a drink. I try to have around half a dozen working on the project, but it still takes a long time to complete.

It took my villagers forever as well and I had about eight working on it. Maybe it's because it's an archeological dig and that takes time.