If they all have the same level of input, then yes.
Which belies the notion that IQ is a sensor property. It is about much more than JUST the sensor. It is about input, signal chain, and post.
Fixed that for you
To say that sensor has nothing to do with IQ is folly. It's like in the old days saying that it didn't matter what film you use. The differences are, I grant you, lesser between sensors than say between Velvia 50 and Portra 400. The capability of the sensor isn't everything, but it is an important cog in a complex wheel. You do need good glass the get the best from a great sensor, but if good glass simply magnifies the weakness of the sensor, then where are we?
It's been a while since I posted, and eve longer since I've shot with a Canon. I now shoot predominantly with the Pentax 645Z with the D800E as my back up. My problem with the 5D3 was twofold: Dynamic Range and the noise banding at low ISOs. I just couldn't live with the banding at all. Lower DR wasn't so much an issue. Now with the 645Z I can push at least 2/3 stops from the shadows with little or no IQ penalty for it. I don't need to ETTR as I have so much latitude in the first place.
Am keeping an eye on developments as I still have the best of my Canon lens setup.
Also on a side note, in forums I see so much dismissiveness about manual focus lenses. For action shots I get the reason for the objection. For portrait and landscapes I don't understand the objection. The Zeiss lenses are superb. I have the 35 f/2 and I'm sure the Otus 55 is mindblowingly good. I wouldn't exclude them because they are AF as a landscape shooter. My 35 f/2 Zeiss wipes the floor with 24 - 70 of any variety at that focal length.
I think you've got the wrong end of the stick. I don't think anyone here is saying the sensor is irrelevant to image quality, nor that manual focus lenses can't be amongst the best - for the quality of the image they produce.
Rather, what we've got is someone claiming the opposite - that only the sensor counts, and that the presence or absence of autofocus is irrelevant to whether a lens can produce a good image. Which of the two is less realistic?
I try to see things from different viewpoints, and I try to give people the benefit of the doubt, but I'd like any neutral observer - expert or layman - to ponder whether the statements 'all images taken by the same sensor at the same ISO have equal image quality' and 'an out of focus image with more DR/lower noise is better than an in focus image with lower DR/more noise' and see if that chimes with their experience and opinion.
If a definition of 'image quality' leads to such absurd conclusions (i.e. in order to defend your position, you have to agree such ridiculous statements are true) then at the very least you have to accept that your view differs from most people's, and is so selective as to be meaningless in most practical situations. Dilbert's entitled to his view, but he has to realise that he's twisted the meaning of some terms to such a degree that few people could reasonably agree with him.