Edit: Forgive me for being "wordy;" I just like explaining everything in detail!
In regards to PvE, be it 5, 10, and 25 mans, both of these abilities I find very clunky to use, especially now that we have a ranged Taunt and Warbringer. One large problem is that what with the mechanics of fights and what I call the "window of opportunity" (being able to actually save someone with these abilities) is too small, making executing their intended purposes require unnecessary micromanaging in terms of GCD usage, positioning, and targetting within a raid. Basically, too much trouble for too little benefit.
In today's raids of AoE tanking/dpsing everything, if a non-tank raider pulls aggro, he'll likely have 2 or more mobs on him and it's highly likely he/she'll be 1-2 shot (recall the very small "window of opportunity.") If this raider is melee, chances are high you're right next to him and thus Intervene won't be available due to being too close. If it's a ranged raider, either he'll be too far away, or you can merely just ranged Taunt/Charge/Intercept the loose mob in question, severely devaluing Intervene. With Intervene you have to be in range of the raider, whilst Taunt/Charge/Intercept you only have to be in range of the mob.
On typical trash packs which take around 40 seconds to a minute or so to clear, burst TPS/DPS tanking is the name of the game since you have the combined might of your raid's DPS bearing down on said mobs. Because of this, the Warrior should be focused on tight rotations and positioning, which leaves very little rage left for anything else. Barring ranged Taunt/Charge/Intercept, Intervene is again clunky because if you have to use it to save someone, chances are high you're completely repositioning the mobs as well, which can lead to all sorts of calamity. Imagine the scenario where a Warrior did this and saved one guy, but since his threat generation was put on halt in order to do this, another raider pulled aggro and got killed.
I would like to think Intervene useful on bosses that someone else is tanking. I like the idea of being able to "save" the MT by Intervening him. But again, the design works against itself here. The window of opportunity to save the MT is too small, especially considering not only might he get healed up, but you would have to juggle to Defensive Stance and likely get 1 shot (which if you're not MTing a boss, that means 8/10 you're in DPS gear, which yes, means you will get 1-2 shot.) Imagine the scenario where the MT was low on health and a Warrior Intervened him, but just before he Intervened, the MT got healed, but the Intervene went off and resulted in the Warrior's death. "1 step forward, 2 steps back." This can easily happen given how many GCD's other people would be using during the time it takes you to swap to Defensive stance, target the MT, then Intervene. I would also be reducing the MT's threat by 10% which again is unintuitive.
On the part of 10% threat reduction from Intervene, it just feels unintuitive and makes Intervene smell of unwashed underwear. Again with the requirement of tight rotations and whatnot, a Warrior tank isn't getting far in the grand scheme of things if he stops generating aggro in order to reduce someone else's aggro by 10%. If you're not tanking and DPSing on a boss in DPS gear, you would have to switch to Defensive stance and lose precious DPS uptime; besides a smart raider would use an aggro reducing ability or slow down on DPS, further devaluing this part of Intervene.
As it currently stands, Intervene is mostly used as more of a way for the Warrior to zip around in raids. Intervene has so much more to offer, but with how it's implemented in-game and trying to actually execute it in raids where it matters most, it is very clunky and sadly relegated to a mere mobility tool.
I would continue on to Vigilance but I'm tired and figured this was enough to chew on and discuss for now. I'll try to add input on Vigilance another day (but feel free to discuss that too!) In any case, what are your thoughts on this and how would you suggest it be improved upon or perhaps streamlined so it doesn't feel like so much of a hassle/fighting against the design/mechanics?
Intervene always been clunky since back when it was introduced you needed a macro to make it useful.
There are situations now though when I use it without targets-target macro, like when zipping around in 4horse-men fight, or on Malygos knocking down the top-threat dps 10% at every vortex.
Unlike BC there are so many opportunities in LK content to use Intervene. Intervene and Vigilance balance aggro and both could be used for hardhitter bosses on MT's as OT to increase survivability. Glyph of Intervene would work fine for that.