I've been using PETG for a while with 2mm glass, nothing on it. The glass is held on the bed with 6 small PETG clips I printed. The bed is at 90°C. I usually use a brim. The prints come off really easily.
I have two pieces of glass. When a print is done, I undo the clips and put the glass on the surface beside the printer, moving it to different areas on the table to help it cool down quickly. Usually I can remove the model within a minute or two. In the meantime, I keep the bed heater on, clip on the other piece of glass, and I can then start the next print whenever I'm ready. I find this method really convenient if I'm printing something repetitively to get the design right.
I've certainly had problems with PETG adhesion when printing a narrow tall model, but for most models it just works.
There's a bit more stringing with PETG than PLA, usually tidied up quite easily, but I'm not printing anything to look good, just to be functional when I find I need some kind of clip for example.
What I can guarantee is that this would not work for everyone. Bed adhesion methods seem to work in very individual ways.