I think you did a pretty good job first time round, and the dithered version also looks good, but I can still see where each tile is, due to the two big stones that you have and the bigger highlights they have, I tried a version making the highlights smaller and adding multiple smaller highlights to the same stone, I think it's kinda helped lose the grid.
The lighting you've done looks good for a top down type of light source, so I'm imagining it more as a floor tile rather than a wall, if it was a wall and it was lit by the sun or an overhead light, I would shift the highlights towards the top of each stone.
Your version on the left + highlights of what I tried to improve