One thing that always bummed me out about coh in the later levels was that when I'd look for teams as a tanker, I would be competing against what felt like an unsaid rule: you only need one tank per team. After all, a well built tank was supposed to handle the whole crowd, keep 'em taunted, and the rest of the squad would mop up.
So- victims of our own success- there wasn't a TON of added value by bringing on a second tank versus another AT- you could get more damage, mez, buffs, from them, but there wasn't usually a good reason to be splitting up aggro by taking on another tank.
Of course, cov didn't really have this since brutes were just total animals with that delicious passive and +800% damage cap (fury+ */kin corruptor+ss rage...mmmm)- and it was nice to have more than one since they didn't have the absolute aggro control tankers did, and regardless they dished a lot of pain.
To me, this is a tough problem to tackle because, while I don't know what the defense/offense balance for stalwarts will be in CoT, all I can really think of is some kind of thing where taunt applies a "mobs take x% more damage" that can stack. or throw more buffs or debuffs into their powersets. But that might be really hard to balance.
*obviously this really only applies to late game 8 man teams: farm teams, TFs, etc., when tanks got REALLY GOOD at tanking.
Maybe I'm mis-remembering, and obviously people were often nice and let you in anyways. But it still felt like there wasn't a huge amount of mathematical merit behind more than one tank per team, esp when scraps could handle themselves and had ST taunt for the occasional extra baddie how wasn't glued to the tank.
Back in my day, taunt only affected one target. We had to take provoke, and we liked it