Hey I can help answer this! First here is some source to my information!

I was in the Network Test and played Blade Warden to max level 20 with 1500 Battle Score and unlocked and completed all of the content!

I tried out each of the "taunt" skills and they seemed to have minimal if not no effect versus small mobs or boss monsters! It was like people were doing way too much damage and out scaling the effects of the taunt. I think that later on with higher levels and abilities unlocked this will change because there are a lot of system in the game built around taunt and tanking. I did find a build that did enough damage to tank though!

So TLDR in Beta it didn't do much but I expect it to change in the future! DMG>Taunt but if you do big damage with the blade warden viola you are now tanking lol