[Kameron8]

I don't really agree with these concerns -- here are my thoughts on each point you mentioned.

I'm aware that Dev mentioned he's planning to buff Black Knights soon-ish or so, and that's exactly why I'm posting this. Silence is a core aspect the class needs and desperately so. Destiny Soldier has no means to stop magic in the slightest. Soldier, Demon Hunter, Black Knight and Tactician have no way to stop a mage.

It's hard to argue that Cobra stance doesn't slow magic down, and this complaint seems centered on the idea that somehow being a Destiny Soldier forbids you from pumping your Resistance. Tactician has one of the best repertoires in the game for spells and skills, and Black Knight is intentionally weak against magic.

The closest you can come to stopping a mage is with Knockdown and trying to run off, but that's not exactly going to work out if you have no means to kite. Unless you've taken Cobra, you're absolutely doomed no matter what you try to do. If you Knockdown an invocating mage, you're left in their proximity to be nuked regardless. If you try to run, they can easily catch up to you by Blinking alone. There is nothing you can really do to take a ridiculous amount of damage whatsoever.

This feels more like an issue with your individual setup, than a weakness of the class tree in general. In no regard are you doomed if you can't kite a mage, and your movement options are arguably as strong or stronger than Blink with access to Charge , Charging Strike -> Retreating Swipe, Winged Serpent, Retaliate, or Hanging. Reaver and Tactician are both handily capable of matching damage numbers against an Evoker, Hexer, or whatever flavor of mage you're facing; again, I recommend you invest more points into Resistance.

Black Knight is also a physical defense class, not a magic one. Unless you're willing to swap out your entire build for the simple goal of being able to resist magic, you're not going to go far when there's a mage in front of you. Magical damage is the go-to choice and with no way to resist it whatsoever, any class with good Magical damage (i.e. Kadouha from Monk), is going to absolutely demolish you no matter what you try to do.

As previously mentioned, Black Knight as a class is designed to be weak against high mobility and magic damage. Your sub-class can help mitigate this weakness, but doubling down on the class' strengths to build yourself an iron wall with no movement options is obviously going to mean you'll struggle in those circumstances. That is by design: a Void Assassin who has a negative crit chance against you, and can't survive a string of autohits, would be in the same position as you are when trying to catch a nimble mage.

Silence is a must. Without it, there's little chance for a Black Knight to stand a chance. My hope is that Dev adds it with the planned Black Knight buff. Without it, Black Knight will just be refrained to be a 'some bonus phys res and some utilities' class. At least with Silence, it can stand a chance.

This conclusion is terribly narrow, and really seems to be drawn off of a lot of faulty assumptions. Silence isn't the end all be all of fighting mages, and there has been a great deal of discussion over the years on how oppressive silence is against pure casters. You're free to disagree with my assessment, but my personal thoughts on the matter are that you are demanding a means to fight against a class counter without having to change your setup to compensate.

Build Resistance, use items that give %resistances, and don't run a Black Knight/Matador DH with the expectation that you can stomp on your hard counters as much as you stomp on the physical damage dealers you counter.