In my limited experience, it's pretty bad. I do not use DL but relatives (with status on DL) do and trying to help them book award travel to India is a nightmare.

The online booking engine is a complete nightmare and often can't even price itineraries properly.

That being said, DL phone reps are extremely professional and well trained. If you have status, you might get a rep who can help you very quickly. People have reported success flying SV via JED. Availability on AF/KL via CDG/AMS is pretty poor.