It's called ... CLANS!

UPD: Next paragraph, "solutions" section title.
Skip to SOLUTIONS section, if you don't need reasoning
A couple of days ago I tried to help my good friend DWLewis to build a castle. We spent several hours doing so - the 2 of us. We got it up to lvl 22. Then jony(1189) came. The rest is history.
I know this is not the only such case, it was no different from other low-level clans' - and some of the first high-level ones - failed projects.
I constantly see complains on forum that this or that class is overpowered/merked, and pretty contradicting suggestions to either strengthen or weaken one or the other.
The game is definitely unbalanced, and the main destabilizer is ... bought levels.
For example, lower level mage can beat sometimes a higher level archer, if the stats are correct to do so. But mages are slower to develop than archers, so in the same time they level less, which balances the game somewhat. Meanwhile levels for both classes cost the same, shifting advantage to mages with level-buying players. But some players are already invested in their non-mage characters - be it a financial investment, or an emotional one.
That's if we're forgetting non-level-buying players completely. If we are not, see this:
I took me about 2 months of many hours a day to get my archer to lvl 150, last 13 of those - completely on spawn parties (meaning fire arrow use on high HP monsters). Sure, it wasn't all grinding in perfect conditions and with perfect stats, but can you blame me for enjoying the game besides grinding?

150 levels is ~2bn XP. Let's see what next couple of 2bn-XP-portions (and time spent) will give me:
34 lvls - to 184 (~4bn total), 26 lvls - to 210 (~6bn PX total), 20 lvls - to 230(~8bn), 19, 17, 15, 15, 14 etc.
So in a year from the point i started playing I will be ... lvl266. Wow! Let's say I'm slow and this is an estimate for half a year of intensive playing. Hmm. With whom can I compete at level 266?
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But even among rich players the difference can be apparent at times. Isoril was 4125 a couple of days ago, and [Link] has sold their buildings - I guess in reasonable fear they were pretty vulnerable in these conditions.
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SOLUTIONS
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The best solution would be, of course, to stop selling levels, introducing instead more uniquely sold gear, undroppable items, resurrect potions, expendable slot drop protection etc. I can offer tons of ideas about what to sell instead of levels. But let's be realistic, this will not happen. I'll even leave it out of the poll.
My second solution is to separate clans on the level-buying basis: clans, who have levels bought among their members, and clans who don't. Clans of those different types would have PvP protection from each other, like regular members. Once you buy levels, you can not join non-payers clan, and are automatically kicked out if you were in one. But I can foresee a lot of complaints from paying players, so...
My third solution is to introduce different clan levels/grades based on highest level of their members. PvP restrictions lifted only inside same clan level. Grades could be powers of 2 times 20 (lowest clan founder lvl requirement) [G1=20, G2=40, G3=80, G4=160, G5=320, G6=640 etc.], or a more sensible scale for upper-levels (every couple hundred levels after lvl 320, doubled every thousand). Buildings level restrictions may apply, as well as crafting level restrictions, so there's incentive to always aim higher.
If either second or third solution is implemented though, players who have already paid for their levels should be given ample time and admin attention to reassign their levels to other characters if they want (all or parts of them), and to prepare new chars if needed, so, say, 1 month?
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Objections, additions? Please vote. And leave comments, especially if you are a level-buyer!