I agree with wiggle room. I dont think that doing jumps and 1/3's on a basic cave cert is wiggle room, it sounds like cave2/full cave to me.
I also see a huge issue with a basic diver doing 1/6ths in a no-flow cave in mexico, and yes, thats "common sense" in that while it may not be explicitly "forbidden" it is not really within the spirit of the standards.
If a diver with 50 dives thinks they are OK diving 1/3's then why not find out and go get the formal training rather than give itg a go and see what happens (and hope their mentor covered the cases when it's especially unsafe to go to 1/3's)
Yes, there cannot be a cert card for everything or else the WKPP or EKPP or many other groups exploring would be SOL
And I agree with your POV on training. I have GUE cave2 and I have turned a bunch of dives for similar reasons....
I also agree that if you have full cave, it's possible with a good mentor to do single-stage dives safely (if you have a good mentor) but you well know that when that topic came up on another board, there were some very (at at least to me) issues from multiple experienced divers on how to dive stages....
For me, it seems pretty clear. Yes, some people may be able to pick this stuff up better than others, but yes training does give a basic minimum standard (in the ideal case I guess), whereas a mentor doesn't really have any standards or anything behind what they are saying.
Just because I am trained to use a stage in a dive doesn't mean I can train someone else how to do it ...
People who want to significantly exceed their training I suppose will always exist, and some may well even scoff at the need for formal training.