Even then, pld/rdm is a defensive combo
For solo/low man I wouldn't agree with this, Dia II plus 16+ per hit from enspells makes a huge difference to damage dealt, especially with Joyeuse. Subbing dancer is for ultra survivability in a low man setting, not red mage. I view /rdm like /war +1. It does more damage.. (arguably) and generates more hate while taking less dmg. That said /rdm does blossom late, 68+ is where it really shines but /dnc is awesome from level 10.
To the OP: if you want just one sub to serve all your needs from 1-75 in a solo setting then it would probably be /dnc. You get acc bonus, eva bonus, subtle blow, almost unlimited curing and erase. The truth is though that different subs are great at different levels, /blu at low levels and /rdm 68+ etc... The problem with /dnc is of all the viable subs it probably has the slowest kill speed. As an example I've been farming Aern's as /rdm, even though they silence frequently, I just blow them away before it becomes a problem and let the silence wear, haven't used a single echo drop in hours of farming. If I was fighting something that could paralyze me though... /dnc all the way.
It also depends on what your duo partner will be, if they're dnc then it's pointless you going /dnc really, if they're able to cast dia then /rdm loses a lot of appeal.