I agree that the net player needs to adjust, but some people adjust too much. Indeed, I think it is more common for the net player to over-adjust than to under-adjust.
I think you have adjusted enough if you can get a racket on that DTL shot with 1-2step. That means you don't have to be standing in the alley to cover the DTL.
Sometimes, I keep a mental score of how often the returner win the point DTL versus how often they miss. I have never had a returner burn me more times than they miss long, wide, into the net or into my racket. The worst I have ever done is a tie, and this is in situations when the returner seems to love that shot and tries it at every opportunity.
My evidence that people over-adjust is this: I like to hit a FH DTL and play deuce court most of the time. I cannot remember the last time I hit a DTL service return. The reason is that most folks alley camp, and if they are going to concede the crosscourt return to me, I am going to take it every time.
-- Random Error Generator, Version 4.0
-- Master Moonballer