I really like the weapon combo on the Scorpions Exarch - I never realized that Biting Blade only replaced the chainsword, so you can indeed take both!
Looks like a fun list. I like the fact that you are taking 2 units of Dark Reapers! I could suggest maybe knocking them down to units of 4, then you could get a second D-cannon in, and have another 20 points to add another scorpion, OR you could use that 20 points , lose a guardian and add a warlock with embolden to the unit - it'll help the tarpit scheme with +1LD and reroll LD tests
DAMN YOU, DICE GODS!