Sololeveling as an ally is not that hard if you only use your brain, it's only slow and can be frustrating at times due to the issues discussed above. If a location x is full of horde and you get ganked constantly, don't be there, change your location and adapt to that situation. For me (lvl 54 warrior), that means skipping some zones entirely and doing some grinding and questing here and there. BS I haven't tried but landing to Thorium Point means immediate death and hope of having enough time to HS the f out there, which kinda ruins the leveling experience but whatever, I have more important things in life to stress about than a game xd. In general, the horde-ally ratio regardless of a zone seems to be more like 5:1 than unity as I rarely bump into other allies.
If you can't handle the heat, get out of the kitchen.