Dreadbore or Bloodchief's Thirst straight up kill a creature or planeswalker, the damage spells will often mean you need to attack a planeswalker even if dealing 2-3 points to it with a spell. Don't get me wrong Strangle is a decent card, but in a deck with black, I would fall on the side of hard removal, another example would be Eliminate

Your sideboard should probably look something like:

3x Portable Hole clear a path/interaction

2x March of Swirling Mist protection spell

1x Kytheon, Hero of Akros  ^Flip value/go faster

3x Thalia, Guardian of Thraben hates on spell based decks

3x Cathar Commando enchantment/artifact hate

1x Lavinia, Azorius Renegade can hate on fires or nykthos

2x Rest in Peace answers graveyard stratagies

So straight away I want to mention Dryad Militant Adanto Vanguard Kytheon, Hero of Akros  ^Flip and Sungold Sentinel Ambush Paratrooper and Zephyr Sentinel are not where an aggro deck wants to be... Arguably depending on what your creature makup looks like Thalia's Lieutenant could also have a home. Settle the Wreckage could well be something you want in your sideboard... A card like Calamity's Wake should really be Rest in Peace and Yotian Tactician should probably be Wedding Announcement  ^Flip

I'd suggest you take some inspiration from https://www.mtggoldfish.com/archetype/pioneer-mono-white-humans#paper

You don't want 4 Kroxa, 2 is the most you want to run... Arcanist Thoughtseize copy is roughly how I would build the same deck. Note that Kroxa and Bedlam are in the main deck, but for game 2, when you could reasonably expect graveyard hate Rotting Regisaur can come in from the sideboard to close out games... Duress is also in the sideboard, for matchups that are less creature centric...

The list may still need a little refinement (Alpine Moon rather than Lithoform Blight maybe), but that is probably closer to where you want to be.

Demilich, as much as I like the card is a trap, something like Bedlam Reveler or Kroxa, Titan of Death's Hunger might serve you better... Without Demilich you could essentially be a BR deck which will be easier on your mana. Mystic Sanctuary and Witch's Cottage potential to be tapped lands makes them bad, while lands like Den of the Bugbear and Hive of the Eye Tyrant are more suited to a low to the ground deck lick this. Cut Down should probably be Fatal Push or Bloodchief's Thirst leaning more to the latter as an answer for planeswalkers as well as creatures... Shrieking Affliction could be something you want, if you are wanting to go down the discard route.