I've done a lot of skilling up both in and out of dungeons with PvM, PvP, and Crafting skills and I don't think gains outside of Dungeons are too slow, in fact if anything I'd say that skill gains in dungeons are too fast. The only time I've really thought to myself "damn, this is some slow going" is when I was Lumberjacking to harvest wood in the 90s LJ, which I was obviously doing outside of a dungeon. I turned my axe away from the trees and toward some spawn (both overland and in dungeons) and was surprised at how rapid the gains came to 99.0, at which point I ate a +1 LJ scroll & GM'd.
With the above stated, I do understand that some new(er) players may be discouraged by the different gain rates/etc, but I'm not certain what the "solution" is to this potenially perceived problem. If anything, I'd say that said newer players should grow some thicker skin, but that's not exactly an attitude conducive to reaching out to new players, especially those who may have had little previous exposure to UO. No one is forced
to skill up inside of dungeons, and I certainly don't think that all gain rates should be increased to dungeon bonus levels.