There is something is don't understand with TK... they have imho one of the best domestic (if not the best) C and *G DOMESTIC ground service (in istanbul and Ankara) With dedicated terminal, dedicated luxury bus etc... but for international i totally agree : the ground service and CS sucks and the overall feeling is "they don't care".
I would mention that the direct lounge access in IST for C and Elite+ (average security + immigration = 3 minutes) IS AMAZING! Few airlines propose this in Europe (except for F pax in dedicated terminal).
For me the main issue is not ground service (even if i really hate how lazy and not customer oriented TGS is) it's the CS = better not to have any kind of issue, because it's a nightmare (very bad souvenir with luggage problems).