Your troubleshooting sounds really good and thorough so I am not too sure where you could go next as it seems you have tried everything I could think of. But are you really sure it is not the Airlink? It is definitely the wild card in your setup, with many people including myself who report performance issues using it for VR (why, I don't really know, didn't look too much into it). But if you Link cable is worse, then there is not much options for you...

I just saw this yesterday where a guy had Link cable issues with the official cable but a cheapo one worked... If you wanna risk a few bucks and try it, maybe it could work? Worst case you simply send it back to Amazon for a refund. This was the one I got and worked fine. It's $20 right now from other vendors but I had gotten mine for $10 when Amazon themselves had them in stock, so if you poke around Amazon you might find another seller selling it cheaper and the specs the same.

Beyond that, I am out of ideas! :(

You can get much cheaper cables that work perfectly fine on Amazon.

https://www.amazon.com/gp/aw/d/B08LL244JW?psc=1&ref=ppx_pop_mob_b_asin_title