I typically only use the guard dog on bugs, since I feel like it doesn't do a lot against the range of the bots. But I did usually bring a shield backpack, so I feel your pain on losing that slot.

Still, I viewed it as giving me an extra stratagem slot to play with. I noticed that the Gatling Sentry puts in a lot of work against smaller bots and allows you to use the Spear to concentrate more on the big boys.