I was in the tile layers union for years and if install properly it should be fine.

At were the tile meets the stairs did you install a metal schluter strip cause that would protect the edge?

also did you put thin set under the cement board before you screwed it down cause that would have added more strength, durability, sturdiness, and would have help distribute the stress from weight.

but if you have a concern lay down plywood. I had to do this on job sites for pallet jacks and those loads were 1-3 thousand pounds, it works perfectly.

also maybe just get a dolly with pneumatic tires.