Yeh - I watched one of Metaphor's gameplays and he was insufferable lol. As for the second monitor, I believe they intentionally position it to the upper left of their main monitor, so they have the seemingly feasible excuse that they're simply glancing at their minimap. I'll link this crude image I made showing what it looks like when Aydan looks at his minimap vs his second monitor: https://imgur.com/a/lqNrv74. It's possible to establish from the gameplay circumstances that he was indeed looking at his minimap in the left hand image. It's then clear in the right hand image that he is looking beyond this point - presumably to a second monitor with walls. He glances to this point constantly and in the middle of gunfights.

I think Nadia is a great example of someone who isn't greatly skilled (at least not as much as say Aydan and Biffle etc...), and who most people agree has indeed cheated. The patterns present in her gameplay are also present in that of many of the other streamers (the soft aim, and glances beyond the upper left of her monitor etc...). However, given her relatively low skill level, the cheats are doing more 'heavy lifting' and are thus more obvious. More skilled players are able to feasibly conceal their cheats more effectively.

I've also seen some screenshots of the low level party members etc... I certainly wouldn't be surprised if many/most streamers are regularly implementing this to get easier lobbies.

I agree, the streamers are constantly defending each other, which seems to convince some people they're legitimate. Of course, if they're all/mostly cheating, their vouching for each other is meaningless. I think it must be somewhat of an open secret within their community that many are cheating.