If you feel like "cheating", there's always the ability to recruit players that already have some gear/experience as well, maybe burnt out on raiding but willing to join if you have that special something.
IE, if there was a guild that started on my server with good leadership, no bad players and only wanted to raid 1-2 days a week, shizam, you've got yourself a skilled, t6 geared tank!
Wishful thinking on my part
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Back on topic, another thing that makes rerolls easier is the spirit buff to priests/druids. It's an extra free 50 mana/5 or more to a moderately geared priest or druid. The difference between a mostly t5 and a mosty crafted/pvp geared DPS class is sub-20%, more likely sub-10%. Good spell rotation/timer usage and maximizing damage between avoiding aoe is what sets great dps apart from good, much moreso than gear.
One dedicated and two moderately dedicated tanks is all you need, this is the only thing I can see holding back a reroll guild's progression - and even then, incredibly skilled healers can work with any tank that can take at least one hit before dying
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