I don't know your activity in your guild, but i am an officer as well, the guy that do the tactics (and i don't forget to include paladin tanking in it

) and a raid leader in my guild and i have found that the best way to prove yourself is by being very active and reliable. Luckily our warriors are not that active, and we have several good and active druids. But the guild was created after TBC launch and while it was difficult at first, i can main tank now without any problems, questions or healers forgetting that i am a tank (got many whispers from healers saying they would never have believed a paladin can tank, if they didn't saw me)
I main-tanked vashj for our progression kill and i'm main-tanking kael for the progression kill as well, getting hit by the first pyro, using shield for the second, the third being always interrupted (40% the other day, should go down tonight. gonna try to fraps it).
It all comes down to skills, knowledge of the fights and activity (i have top attendance and top dkp in my guild). 99% of the wipes are happening because of one or several players doing mistakes and not because of who is tanking the boss. I haven't experienced t6 content, but i have found no real difference in a fight being tanked by a warrior or a tankadin. If the healers and the tanks are good, doing it without shield wall/last stand/tauren racial bonus is not a problem and i never felt like slowing my guild progression.
Except one warrior in my guild that i /roll with to decide who mt the boss (he's less active than me, but in the guild since the first day and we get along well), all the other warriors we recruit are experiencing new things : "oh, a boss, k you are on that add, you on that one, i take the boss" or "hm a threat fight (vr/leo..), k the druid and me will tank the boss since we can generate way more tps (based on previous attempts of course), put on your dps gear". But of course, for bosses like al'ar where i'm far superior in gathering adds in phase 2 and morogrim where i'm the best at taking care of murlocs, i do what is best for the raid. However, i'm already planning to tank a lot of bosses in t6

.
I can only wish you the best of luck, having a server that is tankadin friendly (successful tankadins on alliance side as well) and not very active warriors helps (sometimes we even have to hope one is gonna sign-up to tank sanguinar or make a dps warrior respec...)
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