I think level 55 (using Sewer sets only) is one of the most diverse and balanced levels in the game. There are so many gear choices and specs to work with at this level, which is why I think this is a poor choice to use as an example to support your argument.
That being said, I find this to be too much work and don't necessarily think that it will balance lower levels. If anything, as stated by Kingfu, I think this idea will kill diversity more.
What I would like to see happen, at least in terms of endgame pvp, is something like having certain stats apply in one map but not apply in others. Right now, you get a certain bonus for 2h sets when you enter Ok'tal maps. This means that you currently have two completely different stats on sets when entering pvp and pve at endgame. Perhaps what can be done is to allow stats to be completely different in pvp arenas 77-85 than in pve. When entering these arenas, lower level gear would be scaled down (like 76 Phoenix set) so as not to compete with level 85 sets in those arenas. When entering 77+ pvp zones with 77+ gear, sets can have stats that have been roughly known to work, perhaps with slight adjustments to armor (for the extra skill dmg) or other stats. In addition to this, slight changes will have to be made to skills, particularly from 6-9. No complete overhaul of what the skill does, just some fixes. As cinco has shown in previous balance changes, he's willing to make changes to skills.
If something like this were to work for endgame, perhaps it can also be applied to other pvp brackets as well, at least the ones that need it the most like 66-76 does imo.
No idea how much work this would take, but it seems like somewhat of a reasonable proposal given that cinco has already shown he's willing to make such changes to stats in certain maps like he's shown at endgame with the difference of stats between pve and pvp. Also not sure if the idea is completely solid. I'm just shooting right now.
Bookmarks