The things you described are very interesting, however you didn't provided any evidences, especially about that footage. Do you have a copy of this video?
Topic on User talk:404UNF
Gun Mettle gameplay leak footage
I did provide evidence for most things in the form of source code citations, which is good enough. As for the video, check the history of the Mini-Dispenser article. The link is in there. I had to remove it at the request of testinglol_fp whose stream it was that VNN was watching.
Okay, i've got your answer (for some reason it doesn't appear in there, but whatever). So yeah, the more I'm lurking into leaked TF2 code, the more I'm making sure that everything is true. There's much code about mini-dispenser in dispenser.cpp file, for example. So, I also have discovered a flie "boss_alpha.cpp", where the behavior of this scrapped boss is described. There's no "Level 4 Mecha Sentry" name however, only a link to "models/bots/boss_sentry/boss_sentry.mdl". So probably it's incorrect name, actually I don't know much about that, but still, maybe we should create an article about boss_alpha and include information about Knight and Mecha Sentry in there.
"Mecha Level 4 Sentry" is a name provided by testinglol. I can ask him where he got the name from. Article already exists for it with all the sound filenames from reslists. Toss any other info up there.