Yep it is indeed, no argument there but short of wacking it out and going with an AAV I don't see a lot of options there if there either. I suspect that if it were in my own house I would close my eyes or look the other way and hook it back up again. After all, it was working when he exposed it.
Why not do both? If one hack method that might work is there, why not add a 2nd not great method... bring a tee off the right side of the loop into the cabinet, up a few inches (to get above trap 4" plus), and pop an AAV on that bad boy. Redundancy in hack work is good, right? If the loop fails, the AAV is there, if the AAV fails, the loop may work...
In case anyone missed it, I'm not being serious.
If there's any way to take that vent through the wall and up around to tie back into the original vent, I think that would be preferable. I think it would still be illegal though, to have the vent run horizontal at lower than 42", but it would still be better than what you have, I would think. If you do that, I'd put in 2 cleanouts... one on the sink drain near the floor, and another on the horizontal vent line, just in case you have a backup that gets into the vent horizontal, will allow you to clean it out.
If there isn't a good route, this looks like a good AAV candidate to me though. It seems like you have a reasonable reason to do so. If you do that, cut out all that crap, bring a trap arm over to a santee above the drain through floor, go up a few inches, and stub out over there to put an AAV inside the cabinet, not in the wall. Make sure the AAV is at least 4" above the trap. And as mentioned, check the height of that drain, I think the standard height for a kitchen sink rough in is 18" off the floor, that looks too high.