As someone who has sanded through a few veneers before, you're absolutely right, but unfortunately there's no other solution. The surface roughness is inconsistent due to OP's sanding of the area at 150-grit.

Since we don't know what grit Ikea finished their own veneer to, this is now the new baseline that the whole countertop needs to be brought to.

You're right tho, this might be one of those situations where trying to fix it just ruins it entirely.