I think the fact that, between all of us, we can think of one case where it MAY have happened, proves the point. Yeah, it's probably theoretically possible to seriously compete for a title with just average ATH and DEF, but you would need to (a) be off-the-charts great at probably 2-3 other ratings, and (b) be really lucky in your matchups in the NT. To me, that's not much of a strategy.
The much, much more straightforward path is to build on a foundation of very good (not necessarily elite, but very good) overall team ATH and DEF, and then layer specialized players on top of that (for example, one guy who's a pure point, 1-2 elite rebounders, a couple of big-time scorers, etc.) I think that was billyg's point as well. It's not that ATH and DEF on their own will make you a contender, and there are many different ways to build a winner on top of an overall ATH/DEF foundation. That's where good team planning, the profile of your nearby recruiting pool, and your own personal preferences come in. But it's almost impossible to build a winner without that foundation.