Like with most things, some tankers are better players than others. I'm not sure that having/not having taunt necessarily has a lot to do with it, but I'd agree that, having picked taunt and then not using it seems... pointless?
My SS/Invul doesn't have taunt, and probably won't ever take it. I mention 'NO TAUNT' prominently and early in my search comments (maybe I should have just named him 'Tauntless'?) I have never ASKED to be on a team, so if someone doesn't like it - well then, DON'T recruit me, and if they do, don't then be giving me a hard time about it!
As to why I don't have taunt? Well, firstly I tend to solo a lot, and taunt is about as much use to me solo as an ashtray is on a motorcycle. As a result, my tank is more of a 'scranker' build, also mentioned in my search comments, so, 'let the buyer beware'.
Why do I solo? - well, sadly, most teams I've been on have been pretty disorganised, and many seem to have absolutely no idea how to use a tanker. My tank has never once faceplanted solo in 41 levels, he only EVER dies on teams. Even without taunt, teams usually seem to need me a lot more than I need them, and if they were prepared to learn to work better with me they'd still find me very useful.
I can't count the times I've been the teams only tank, been asked to take point, and have then had an un-stealthed/non-invisible team mate run ahead of me and accidentally pull uncontrolled aggro (I have stealth myself for recon purposes) Anyone who gets ahead of me and draws aggro in these circumstances deserves all they get, and I'm certainly NOT wasting a power pick to save their sorry behinds!
The other classic is when I've been asked to take point and pick a route and the leader has asked the party to follow my lead please. So, I set off only to see on my map that some of the party have split and gone exploring somewhere else completely... taunt is unlikley to save THEM if they get into trouble, and I really don't see that as my problem anyway.
As to trying to explain to people that I need a few seconds alone with a mob to get them focused on me.... waste of breath/bandwidth usually. Again, I can't count the number of times I've been about to contact a mob only for someone to fire at them or worse, unload a big AoE before I can land a punch. Exactly which bit of 'wait please' was unclear? Again, I'm not wasting a power pick to mitigate other peoples stupidity.
Conversely, I've never found my lack of a taunt to be a problem with sensible payers. I have a ranged attack (hurl) and a PBAoE which work just fine as openers to get the bad guys interested in me - as long as no one else gets trigger happy first.
My normal tactic in teams is to target the toughest bosses/Lt's in a group (especially Mezzing types etc.) and focus on shutting them out of the fight whilst keeping their attention on me and away from the team. I hardly ever bother hitting minions and rarely put 'finishers' into cripples when anything tougher is on offer. With Gauntlet and all the knockback/disorient effects of SS I can comfortably keep 2, sometimes 3 boss types totally occupied almost indefinitely, usually along with quite a few lower level goons besides, as long as no one else interferes. Oh, and I always try to stay aware of my teams status (Invul/SS tanking is rarely very frenetic, too easy to punch yourself out of endurance if you go bonkers) So, if someone needs help I can almost always go over (combat jump works well there) and just punch their oppressor off them. I've yet to have a mob continute persecuting a team mate after I've smacked the offender upside the head! - I can't fault gauntlet there. If a 'squishy' has somehow got themselves into a whole heap of trouble with multiple attackers, then IMO opinion they've screwed up. I'll still go over and help out, but again, I'm not taking taunt just to cover their mistakes.
I'm not saying taunt is useless, just that IMO it's not the be-all and end-all of tanking. I don't claim to be an uber tanker, I'm not, I'm a 'scranker' first and foremost, though I CAN tank competantly in the right circumstances. Teams that are down with what I'm capable of can and do get decent mileage out of me, and can count on the big nasty types leaving them alone if they let me do my thing. Teams that aren't, or are incompetant or inexperienced? - well, I really doubt if having taunt would help much there.
