1) I went out earlier and did a number of fights on Dark Knight just to play around with it. Was easily able to quickly solo skillchain them down without them getting any TP move off, which was what you were touting was something that Sch could do that most DDs couldn't. A quick Scourge to Resolution dropped the Twitherym without any difficulty. In fact, I think it probably hit me once the entire time, that was it.
2) Yes, you do have to worry about the monster going yellow. You're going from a situation of weaponskilling it to close a Darkness skillchain to running away and kiting it (which is what you say you do). If you manage to pull out just ahead of it to where you disengage your weapon, which varies for each mob, then the monster is going to go yellow. That's just the mechanics of the game, and it's really not hard to run far enough ahead of a mob even with just normal 12% movement speed. Even if no one steals the mob in that time that it's yellow, if it dies while yellow, then you're going to lose everything that would drop. A mob dying to a DoT while unclaimed results in you getting nothing out of it.
There's a difference between the Ninja situation and this one. Ninja has/had all the tools necessary to be able to tank effectively. They had the enmity generating tools, the damage mitigation tools, and the hate maintaining capability to make for a good tank, and Square Enix has since accepted Ninja as a tank job. People were quick to jump on Ninja for tanking purposes because it could do it and do it well. Scholar though isn't an effective melee DD, which is why its only real purpose for a good while was as an Embrava spammer. If it had the potential that you claim it does, then believe me, more people would be doing it, but it just doesn't.
I mean this in the nicest way, but if players are wanting your Scholar over your Dark Knight for melee purposes, then that's more a testament to the quality of your Dark Knight than the capabilities of your Scholar.
Play a job you want. Sch can open up doors but only if you gear it well and don't let noobs tell you that a job can't do somethingit clearly can. This coming form the guy who didn't understand how to play blue and has no concept on how to play sch. To that justification, he can play drk better than I.
If that was meant as a quip towards me, I'd like to point out that not only on this forums but FFXIAH as well, you've been pointed out by numerous individuals as having a lack of understanding on the basic capabilities of Blue Mage. Your recommendations on weapons, gear choices, actions, etc just don't work when compared to established best actions, and this is one of the reasons why people don't accept your claims as to the capabilities of Scholar.
I won't name names, but there was a forum user on here several years back that was adamant about Whm/Thf for everything they did, and was insistent that it did better than all other combinations. It didn't matter how much evidence was shown to the contrary or how much people demonstrated it wasn't as viable an option as they claimed, this person was adamant about using it and only it. They'd make lofty comments about what they were able to do, but would get defensive when asked for proof. Your approach to all this is pretty much the same.
If you want people to believe you, then you need to show actual proof. I've asked before for you to show or list off what gear you use on your various jobs, but you never do so, and instead berate myself and others for doubting your claims. The burden of proof is on you in this case.