BTW not everyone wants/needs paper-thin DOF. For my advertising work I shoot a 5D3 at f/8 to f/16.
Fine, but although 85mm on APS-C gives the same FoV as 135mm on FF, the 85/1.8 on APS-C gives the DoF of ~f/2.8 for that same FoV. If you want the equivalent of 135mm f/2 on your APS-C, you need:
3. EF 85mm f/1.2L II USM - Max. Diameter x Length, Weight 3.6" x 3.3", 2.3 lbs. / 91.5 x 84.0mm, 1025g
...and the 135L on FF will give you better IQ than the 85L II on APS-C.
What's so hard to understand? I shoot my advertising work at f/8 to F/16 with a 5D3. Clients like their customers to get a clear view of their product, not some arty blur.
IQ, you've got to be kidding, I've shot ads with a 40D using an F/1.8 85mm lens set at f/16. Were not talking about HUGH prints, just full page magazine work (print = about 150 DPI). If I was interested in High IQ I'd shoot chromes with my 4x5 or rent an 80Mp MFD (with a 240 mm LS f/4.5 IF leaf shutter lens.).
Different strokes for different folks!