1. Full offtanks - maybe. But still, even if you somehow manage to deal max damage to this tank (you will not) as 4k FA+2-3k FTW it will not kill him with full hp. If someone is assisting you - then maybe.
2. And your opponent will be drooling and watching while you are closing in to use your debuffs, right? Yeah, randoms usually do exactly that. But good groups will focus you down the moment you come too close - and yes, 65ft IS too close sometimes - the moment you are ready to use your healing debuff you may find yourself being pulled/full of dots from SH/sorc. Its nice and all to fight against randoms, but in really serious fight you are not that great.