On the scale of Houzz horror stories, this is hardly a folk tale.

Yep. Just live with it.

Mosaics like the tile you have come pre-spaced on sheets. A good tile setter might adjust a tile here or there, but please don't hold them accountable for reconfiguring a bad sheet. Maybe they should have culled some sheets, but that delays the job and the cost to return when replacement materials are available ultimately comes out of their pocket.