My own experience:

I currently fly YYC-FRA-TXL approximately once every six weeks. At the end of the flight there is a three-hour drive to a point between TXL and POZ. The usual layover in FRA is four hours.

Could I do it in Y? Well, it may be possible.

Would I do it? Not if I could help it.

At a bare minimum, I would insist on a day to acclimatize, so the client is paying for an extra day of my time, plus a hotel room in TXL. The difference between discount J and discount Y is considerably narrowed once this is taken into account.

Plus, as mentioned, it is a perk, and softens the blow of fourteen straight twelve-hour days.

Now, my time and expenses are billed directly to the client, so J is not a cost centre to my employer. It is standard in our contracts, though, that flights outside NA are in J, and none of our overseas clients have objected to this.

And don't even get me started on YYC-FRA-DXB-MCT; trying to mandate Y in a case like that would quickly lead to "Find someone else" from most of my colleagues.

YMMV.

Best regards,

TB-ES