I'm not sure about all this, but here is my experience.
I play a lvl 27 Ranger, and have solo-ed 80% of the time, albeit i have played for about three weeks. Things have always been hard, but there have been many a kind person go out of their way to help. However, I never take a yellow by myself, only deep blue cons. I can only single pull 1 deep blue and survive. 2 deep blues and i'm usually dead. I can double pull a deep blue and a light blue and survive. Then have to med, i'm careful about where i sit in dungeons, and hope for no pops.
If my bow hits a deep blue on a single pull, im fine and can take another single deep blue right away. But my archery is only 100 (for now), and even with a fairly nice bow, roughly 25% I miss. Of course Melee misses fairly often too, with 135 1hs, but my dodge, kick and parry, help to negate the misses. Also knowing when to change styles, which i admitedly am still learning, can help.
The bigest thing that i find is to explore WR. There are many more places after lvl 10. At lvl 13 i was always in warrens, im lvl 27 now, and i still go there and single pull deep blue cons for 4% exp. But there are other places.. At lvl 17 i went to echo cave, toward the zone line for fungus grove i found bugs and shrooms, all single pull deep blues yeilding 5% exp. At lvl 27 the bugs are green but the shrooms in echo and fungus grove itself yeild the same 5% exp.
Yea, it's slow, but it's not unbearable. Go other places and hunt. Solo, duo, whatever you can do. There are sky drakes in GD 5% exp, there is echo, warrens, shrouded isle, and there a couple quests, all by lvl 20. I'm finding more mobs to kill here and there as i reach lvl 30, all giving atleast 4 or 5% exp. Venturing into Bancak, Fungus Grove, GD, wandering warrens and finding kodiacs, grouping in FR when i can, and looking forward to EW, Neth, FW, and The Barrens.
I solo where and when i can, i die alot, i pay it back, and work for another lvl. And when i find a group occasionaly, we take on yellows and reds and lvl up just like everyone else.
I expect to have to spend time raising a char. For then there is achievement. Yes, it could always be easier and faster, but of course then the end result would suffer (much like fast food).
But then again wth do I know, for after all I am the Uber Noob.
~Darkartist