Wow, thank you. Learn something new everyday.
Good news is for sheet there is probably no reason I can’t use mild steel. Obviously chassis/cage/etc need to be a chromoly but most brackets etc that I need to make out of sheet do not require the same material properties.
Fortunately I have access to a waterjet (how I have done these parts for 10+ years) so when I need 4130 I can have it done there.
Sounds like I need to upgrade my consumables though!
Update for all those that spent time helping
I replaced my torch head and consumables with stuff from @mechanic416 . It absolutely cuts better than I expected! Note I did switch to mild steel, but that was certainly only part of the issue.
Summary: spend a few bucks on good consumables. 
I’m no expert but it looks like cut height to me. I’ve made similar cuts and it turned out to be my torch height, my Z axis would bind and the torch would be cutting from a height greater than .25 a 1/4" and resulting in similar cuts.