Will a thin or thick cutoff angle grinder wheel last longer?
Cutting disks should be thin. Grinding disks are thicker. Thicker disks means removing more material, which takes more time. Typical disks in Europe is 1mm thick, and I'd categorize a 1/8" (3.7mm) as a hybrid, usable for both cutting and grinding, but not excellent at either.

A thinner disk also leads to less heating in the material cut, as less energy is deposited.

In addition the disk should be made for the material you're working with. Different materials behave differently.