To put it simply - lasgun right now would be every general's and soldier's wet dream - roughly the power of .50 cal (can blow off limbs in one hit) while still in the standard rifle size and weight, basically 100% accuracy, huge magazine which can be recharged in multiple ways including throwing it in fire (literally) thus easing logistics a lot, etc.
Problem is that every enemy is 40k is over the top in some sort of way and wielding stupidly overpowered weapons when compared to the lasgun.