Defense is important, but not the most important factor.
I tend to end up with teams that are defensively superb, but offensively inept, and what I notice is that this is just not optimal. I was not winning many games.
Balance between the two is important.
For offense, you should pick one offense and do it really well. How exactly to do it really well is often debatable, but what I have noticed is that it is better to have 2-3 capable scorers for that particular offense, than just 1 terrific one with the rest at sub-par.
This is just my opinion, and please accept a disclaimer on that, as I am not all-knowing or perfect. But I hope this helps you out in some small way.