Now I know that's a tough suggestion to follow-- even I, despite being driven so nuts by this, have wanted to try out my new spells so much that I've taken some level 44s and 22s into the battlegrounds. But the fact is that at the lower end of each ten levels, you're just not anywhere near powerful enough to either do much or survive in a BG. And the people that did show up to play at 29 and 49 and 59 are just being left shorthanded by having lowbies on their team. Maybe teamwork can help a lower-leveled team power past a team of 8s and 9s, but since teamwork is missing in most PuG battlegrounds, I haven't seen it yet. And yes, a well-timed root of any level, or any other utility spell, can save a BG, but it wont if that root gets resisted.
Is there a fix that Blizzard can implement? I don't think so-- even if they gave 9s their own BGs, then 8s would complain, and even at 70, gear can be so inconsistent that it still doesn't matter that everyone in the BG is the same level. But if your level ends in 1, please don't even bother going into a BG-- go level up (leveling pre-60 is super fast now), and then come back to actually help your BG team win.