Interestingly, I recently tried to dive in and figure out why exactly Microsoft went with COFF. It seems like Intel OMF was adapted all the way up through OMF386, and Microsoft switched to COFF around 1989, near the beginning of the NT OS/2 project. Fascinatingly, it seems like a big criteria that Microsoft had factored in was that tools for COFF already existed for the Intel i860 RISC processor, so early on in NT's life they seemed to think that it was going to be a lot more important.
That said, I do not consider PE to be similar enough to COFF to warrant calling them the same format. Aside from having completely different headers, PE has many additional structures that don't exist in COFF, and even the structures that are shared are fairly different between PE and COFF. PE barely uses anything from COFF, and it doesn't even use it the way that COFF does. Of course ELF objects also have some differences between object file and shared object/executable, but it's at least very clearly the same format the whole time, just utilized a bit differently.