Hope you don't mind if I ramble here.
General EDH deckbuilding guidelines I like to follow (courtesy of the Command Zone podcast):
10 card draw
10 ramp
5 spot removal
5 board wipe
38+ lands
You don't need to use them, but I find that it helps a lot when I follow these guidelines.
On to other suggestions.
Does
Arrogant Bloodlord really work in EDH? I would think it would run afoul of tokens.
I have a 60 card knight deck that likes to run
Concerted Effort to take advantage of the various keywords that some knights can get like
Skyhunter Skirmisher.
For an EDH deck you can't build it as part of your key strategy, only being one card and all, but it could be fun.
Similarly
Odric, Lunarch Marshal does the same for a few other keywords.
Thinking about how EDH tends to play out (at least in my playgroup), you may wish for some larger/flying/evasive knights, such as
Drogskol Cavalry,
Deathless Ancient (you appear to have a small vampire subtheme), or
Knight of Sursi.
The other thing my 60 card knight deck likes to do is run
Weight of Conscience. Tap 2 knights to exile the enchanted creature, then use
Sun Titan to repeatedly bring the enchantment back. It's not going to be a consistent method of repeatable removal for you, but it's an option (admittedly probably worse than Haakon+Crib Swap).
Stillmoon Cavalier is absurd.
Dauthi Mercenary and
Soltari Crusader avoid most defenses with the potential for large chunks of damage.
Pfffft, I forgot about these next ones:
Eastern PaladinWestern PaladinNorthern PaladinSouthern PaladinPentarch PaladinBe warned though, those critters may well put a target on your back, particularly against multicolored opponents.
Kabira Vindicator is another anthem on a knight.
Knight-Captain of Eos+
Elspeth, Knight-Errant, or better yet
Elspeth, Sun's Champion, is a VERY solid defensive position to have (until the inevitable board wipe anyway).
Knights of the Black Rose is a personal suggestion from me because I love what the Monarch mechanic does to a game of commander, really moves the game along.
If you enjoy thoroughly breaking the color pie there's
Order of the Sacred Torch.
Zhalfirin Commander for more knight tribal synergy (though it may not be efficient enough to be worth it).
Auriok Steelshaper is another potential anthem.
Waylay for flavorful ambush tactics (can also be used in conjunction with Aryel's second ability to take down bigger things).
Magewright's Stone more activations of Aryel
Thousand-Year Elixir more activations plus earlier/faster activation