This is all assumption from me, but I think a lot of testing would likely be diagnostic machines and specialized testing – not actually playing games. I would assume it’s something like plugging in, confirming the parts all meet spec after whatever the refurb is. That spec is probably more around frequencies, power use, temperatures.
Obviously that’s not good enough if they’re sending out these clearly broken refurbs.
Unless something has changed very recently, Destiny 2 does not work under Proton because the Anti-cheat isn’t compatible. Windows is an option, but I’d really recommend a dedicated Windows handheld for that instead of the Deck.
I haven’t tried Windows on the Deck itself, but based on 6800u performance, you’re looking at maybe getting a solid 30fps on lowest settings. Destiny 2 is not a very well optimized game atm, and even the Ally at 20w can have trouble holding good performance in Neomuna or the Tower.
Sure, they obviously are dropping the ball here, just trying to explain what they might mean by “thoroughly tested” and why it’s not succeeding