Then I can only reiterate, as one playing on Tactical, that this is your problem.
Not really. A lot of people like the original poster noticed the difficulty to "properly" tank in the game. There are already many topics on the forum like the ones saying that taunt should bypass the physical armor or the need to add the reverse stench skill, etc...
All those thoughts are born from the same initial observation : "Tanking is not as efficient as other playstyles".
A lot of people notice the "difficulty" with just about anything, especially when it comes to Tactician.
Whole taunt thing is just a dumb gimmick, I already told you how you can shake off things off your squishies and make tank take it instead - it involves proper positioning and removing other viable choices for enemies which is not really that difficult to do with a bit of planning and yes AI is built to counter that and it's a good thing, as opposed as some cheap shit like taunt which basically shuts it down.
Things like having your team on higher ground with a layer of slow/CC walls in between and removing threats gunning for squishies will make AI focus what it can then, which will be your tank if you play your cards right. And no it won't be 100% focus, but it won't be ignore at all.
You have smarter tools and ways to shift attention and it is up to you to utilize these.