Grinding disks and ufh cables won't end well, if there's a gap under the straight edge it needs filling. Mp3 has never leveled a floor before and the first attempt using the spiked roller didn't go too well, so what's the point in going through all that again. Imo after marking all the dips out a long straight edge is the best chance he's got at getting this floor tileable..
No im not saying he should grind. Was just pointing out about other tilers ive seen thinking it needs more SL rather than grinded.