If sapper gun has no range limit/spread then it would be very overpowered.
A good engineer already builds his sentries where snipers can't get them. The red beam will give away the spies position.
paralysing for 10 seconds with a stab anywhere on the body i think is a bit imba aswell.
Only crits would cause that and remember the stab is 20% slower so will be harder to stab.