So you have a W/B aggro shell here, but are leaving out all of the Aggro elements past your one drops. You also have quite a few cards that just do not fit into your plan and, in many cases, actually work against it rather badly. For instance, sure, you can rely on Athreos triggers to try to take people out with Drown in Sorrow, but if the biggest threat you have is a 2/1, they'll just let you get them back and beat your head in with a 5/5.
So, what can be done to improve the list? More aggro, more anthems, more ability to alpha strike.
Out:
-2x Thrill-Kill Assassin - you want more out of your two-drops and you most certainly don't want deathtouch for blocking (as you're not in the business of blocking)
-2x Fiendslayer Paladin - he can go in the sideboard
-2x Sin Collector - again, sideboard card
-1x Xathrid Necromancer - this is iffy, but going down to 3x won't be that bad
-1x Teysa - she's an EDH card, sorry...
-2x Silence - you could try this being really aggro, but I doubt it'll perform unless you run 4x of them main - and even then it's kinda iffy
-2x Drown in Sorrow - a board wipe is the LAST thing you want
-2x Diabolic Tutor - this is far too expensive and has zero impact on the board on T4 when, in reality, you should be about to win the game
So that's 14 slots we've opened up...
In:
+2x Dryad Militant - gets your count of one-drops to 10, making it a near certainty you'll hit at least one every game
+4x Daring Skyjek - tons of power for the cost, you're going to be hitting battalion quite a bit, evasion, etc.
+2x Spear of Heliod - who doesn't like a good anthem?
+2x Hall of Triumph - Given that Spear and Hall are both legendary, the 2/2 split will give you a decent chance of making sure you hit at least one, if not one of each. An argument could be made to even kick this up to a 3/3 split.
+4x Brave the Elements - protection against damage, and, most importantly, a way to sneak that last damage in with an alpha strike
So that makes 14 to go back in.
Arguments could be made for quite a few other cards, but in reality, this will DRAMATICALLY improve the deck while costing somewhere in the realm of $6-7.