If you go back a couple years, the only team with a smaller coaching staff than the Steelers was Belicheat's Patriots.
It would seem that a team's success doesn't depend on the number of assistant coaches they have.
And yes I know Belicheat doesn't have much of a coaching tree either but he does have a bunch of SB rings.
Shades' tendency was to only hire assistants that either he knew or worked with before. It makes me think that he wants things his way and doesn't want to be challenged with new ideas. He would also keep assistants who weren't very good at their jobs, he seems to be the type that doesn't like to hire new people. Keeping someone who sucks at their job is preferable to going through the hassle of hiring someone new. We've probably all worked for someone like that.