I'd question your decision to dismiss the Widowmaker out of hand. The situational crits on the Frontier Justice are nice, but I'd argue that the ability to pump shot after shot into robots, continuously, without reloading, and (especially when you factor in projectile penetration) get more metal/ammo per shot than you started off with to boot is a lot more versatile and may well end up doing more DPS in the long run.

That aside, decent guide - if nothing else, anything that helps to drum the importance of upgrading dispenser range into the thick skulls of your average MvM Engie is always worthwhile.