I don't understand your point here.
Nowhere in their website they are claiming anything about how they price their tickets so your AAA-BBB-AAA example is irrelevant.
Of course married segments are common. I have no issue with married segments not in any airlines and not even in TK. They are not claiming it's not available, the agents claim that this J is a different J and that is ridicules.
If they put a statement on their website which they followed (up until today) then to me this a scam. I had no issue whatsoever if J was simply unavailable and other buckets were available to sell (like any airlines does).
My point is simple. If TK don't want to sell J from your preferred departure point to your preferred destination, then it's not a scam. The fact that a third-party (or even the phone agent) suggests that there might be J bucket space available for components of your route is irrelevant as you are asking the agents to "travel hack" their own computer system, which they are unwilling or unable to do.
TK can sell J fares from AAA-BBB-AAA but not for BBB-AAA-BBB. Their call, but certainly not irrelevant.
TK agents aren't very good. Agreed. Making up weird excuses... Not good but again not limited to TK.
I would also love a TK website that actually displayed information in a sensible manner. Barring that, the old website would do just fine.