Yojimbob wrote:"Easily" is a bit of a stretch since it's ~7.40% for a SM and ~5.55% for a guard to shoot and kill an xv8 with a single shot. Expected damage per shot is ~1.55 and ~1.16 respectively so you CAN expect them to tank several shots per guy before they bite it.
I'm pretty sure the numbers work out even better in the Lascannon's favor. Seeing as a Space Marine Lascannon hits on 3s, wounds on 3s, the XV8 gets a 6+ save, and 2/3 of the damage results one-shot the XV8.
Multiply it all together, and we get (2/3)*(2/3)*(5/6)*(2/3), or 24.96%. A one-in-four chance of one-shot killing an XV8 is not a chance we'd like to take. To make it worse, Imperial armies don't tend to field single Lascannons, but rather whole banks of them at pretty low points costs.
To make it worse, Mathhammer looks nice but things rarely work out so neatly on the tabletop. 25% is mathematically unlikely, but we all know how easy it is to role a whole string of 3+s in a row.