NLRMs are possibly the worst tech ever introduced into the game, in that there was absolutely no place for them in a timeline where Clan LRMs are widely available. All they did was bloat the equipment charts with something that is outclassed by pretty much every alternative.
If I was redoing the Dervish, I'd go with paired ELRM 10s, and figure the rest out from there. I understand the reasoning behind the WYSIWYG requirements, so it doesn't much bother me. It can be viewed as a restriction, or as a challenge to your design ability. I love some of the wacky stuff it's led to, like the Crossbow T, or that Shadow Hawk with the five Thunderbolt launchers.