Afish will be along shortly to lend a unique crotchety old man take on why won't you people fish modern technology. I like to hope he quotes my post and belittles it as much as possible, it's like our special game.
That said, what he will inevitably (correctly) point out is that DT and WF lines are the exact same thing for the first 30ish feet or so.
It's only have the head in a WF line is done and it tapers down to a running line that a difference is found.
So, are you rolling casting past ~30' of WF? Then you're hurting yourself as the running line's lesser mass won't carry the energy down the line (esp as it increases mass into the head). However, if you're not casting into the running line, then there's no difference, and you simply need to get better.
The same theory holds to casting line in the air; the difference here is that the DT line will carry more weight in the air (and also bleed energy quicker). YMMV, but at typical casting distances for trout feshing, they work the same. If you need to shoot beyond 30' of line, then WF makes sense as the increased mass alone in teh head carries the running line bette than the uniform thickness DT line does.
The triangle or whatever it's called lines roll cast the best (and cast better, too) due to the fact that its a constant taper forward, so as the line thins out the remaining energy you put into it continues to push forward.
Finally, fiberglass normally roll casts better than graphite due to the way it flexes and transmits its energy. You simply need to get used to the different timing.
