I personally don't agree with the statement that nomod is the best practice and the argument of "DT/HD/HR doesn't help you increase skills".
For me, in order to improve, I usually do whatever highest nomod fc I can do until I can't squeeze any more pp out of my hands --> play DT on lower, much lower maps that still give pp --> play HDHR on higher maps I've already fc'ed --> nomod.... over and over again.
Except I can't HDHR/DT maps I do nowadays so I've been sticking to nomod.
Nomod helps map reading and helps hone basic skills, while other mods help different advanced skills such as reaction time, memorization, etc...