Thing with champ tanking is that agro is never really solid. A champ builds agro through dps, and through getting smacked in the face (because of the reflect). Because a large chunk of the damage comes from Riposte though, and in most boss fights nowadays avoidance is useless, we don't get the parry procs we need which forces us to rely on force taunts more than we should. In AoE fights and taking on trash mobs, agro is fine in my opinion, but once we lose parry procs, we fall short.
In my opinion, blue damage should be increased, especially on Raging Blades and both Horn skills. I think blue should do about a third to half the damage of a yellow champ, making it do considerable damage for a tank because to me this is where the color is for a blue champ. The reason to take one would be to get more damage. Currently, however, damage is not in a good place in blue line. About 20-25% of our single target damage comes from autoattacks (in my experience), which is kind of a ridiculous amount to me. In my opinion, the biggest threat skills should be Raging Blade and Horn of Champions, followed by Riposte, Blade Wall, etc. Blue champ really suffered with trait trees because of how integrated other "red" and "yellow" skills were to holding threat in this line, and this is something that needs to be addressed. Either the baseline for these skills needs to be increased regardless of traiting, or blue line specifically also needs to give an extra boost to these skills.
One thing I always toyed with, but never used very much was a blue/red build for boss fights to tank through strike skills, but because of partial avoidances and the lack of the better Battle Frenzy from yellow, the damage never really made it worthwhile. One thing I would like to see would be having Fervour actually matter again, rather than being forced to put 4/4 points in Battle Frenzy in yellow regardless of how you trait. Increasing Fervour generation in all three lines in some form or fashion and getting rid of the 10s version of that skill would be a step in the right direction in terms of gameplay if you ask me, so long as the Fervour generation doesn't get out of hand like it is right now. Actually having to manage it would make the class more interesting.
In an ideal world, we would do enough damage in a tank build to hold agro on a raid boss without taunting and have another cooldown or two for when things go sideways, but the changes made to blue in my opinion are a step in the right direction. I would just like to see Raging Blades and especially both horn skills (Horn of Gondor/Champions) be more meaningful for building threat, along with seeing a few changes to traits that I've mentioned in other posts. Also, getting a bit more of a benefit from Adamant, Unbreakable, and Bracing Attack would be nice to provide actual cooldowns to use (Dire Need still needs to be increased for level cap, I've made posts about how to do this without breaking it for lower levels previously in this thread and in the Champion sub-forum). If those things are accomplished, I would call blue champ "finished".
Other post
here for Blue recommendations.