The 70-200II is not better than the 135L for IQ at any aperture.
True...but nor is it worse (Klaus at PZ gives slightly higher numbers to the 70-200 II across the frame at most apertures, although probably not real-world relevant). That being the case, from an optical standpoint the only benefit to the prime is that it's one stop faster. That can be very important in some situations, but the zoom certainly wins on versatility with no sacrifice of IQ.
It has slightly less vignette @ 2.8 but that's about it. Neither are terrible lenses but to claim either is vastly superior in IQ is nonsense.
The prime certainly wins on speed, weight, bulk, price, and stealth. If only it was a bit faster and had IS.