General contractor markup for tile installation?

I'm in the middle of a full kitchen remodel with a GC. The cabinets are installed, and we're currently waiting on countertops. Remaining work includes appliances, flooring, backsplash tile, paint, exterior brick work, and a window install.

I'd like to delay the tile and paint until after the kitchen is functional so I can live with the space and decide what I like. My GC said he'd need to check with the owner if that's possible. I'm also considering asking to remove those items from the contract and I'll higher a tile installer separately later, but idk if the GC will agree to removing these line items from the contract.

Originally, the backsplash (countertop to underside of the cabinets) was quoted at $2,650 for labor only. When I asked about extending the tile to the ceiling on one wall, the revised labor quote became $6,450.

I also got a quote from a highly rated local tile installer for the same scope, and they quoted $3,260. That's about half of what my GC is charging.

Assuming my GC's subcontractor charges something similar, that suggests roughly a 100% markup. Is that typical for tile work? The markups on the other subcontracted work (electrical, masonry, cabinet installation, etc.) don't seem to have been nearly as high.

Note that all of these quotes are labor only and exclude the tile and grout materials.

Here's a pic of the 3 walls that will be tiled:

1. main wall from countertop to ceiling: https://imgur.com/KnYsMjX

ceilings are about 98" high. horizontal dimension of this kitchen is 156". those 2 windows are each 36" x 38".

2. this wall will remain countertop to bottom of cabinet https://imgur.com/SZzgqd4

3. this wall just that small patch to left of fridge (ignore the cabinet circled in red. idk how to remove the circle) https://imgur.com/Mnwv7nc