I never said TK is a bad carrier, but they are not LH level either. The way to tell is to see how they handle a situation when things go wrong.

Anyway, back to TK and *A. Few examples:
1. I tried booking a flight from TLV to Japan (one of the smaller cities, which required a leg with ANA). Could not find anything with TK (they could only get me as far as Tokyo), booked with LH and ANA.
2. My agent explicitly told me that combining TK and LH tickets is no go. What is interesting is that apparently it is not just LH (see above)
3. Whenever a flight is delayed and one of the *A carriers need to put me on a different flight, they are extremely reluctant to use TK

I may think of other examples, but I think this clearly shows TK is mistreated - not just by LH, but by many other *A members too.