That knight guy is somewhat rough for melee, but you can joust him to death with any decent reach weapon especially if it has bleed. He is a total pussy against certain weapons you likely have at that point if weapon arts are your jam. The lance from the capitol (or the shooty spear in the deep underground) put him down pretty fast and are both good weapons against Malekith on top of that. The weapon art from the snow area that makes multiple copies of you in a melee chain is also really good for bosses like this.
Twin Gargoyles always manage to piss me off, though. The Camera is not what pisses me off as much as the poison death cloud you can't really clearly see. That and I hate DPS fests, which that fight is really about burning one of them down asap. And just about any weapon that might be effective in that fight is pretty much only obtainable after you beat it unless you are going to beat all of the lake area before tackling the fight. Probably the most poorly tuned fight in the game, in terms of when they expect you to try it, especially as a Melee if you are not twinking. And of course they are immune to everything and resist any damage that's not strike, so if you are melee its hammer time. And do not overcommit to attacks because they will do the fucking spin move or poison your ass while you are stuck in a long combo animation. Get a hit or two (or a Jump) and back out.