In 75 there is not enough data yet to know which plays will work for you or not, offense or defense. Most of your players are probably still learning the plays to begin with.
In a new league, such as 75, I usually pick my plays for offense and defense, and then don't change them at all until I have used them for a season. There are some plays that may work for others, but have never worked for me, so I avoid them by default. I try to have a variety of plays from every formation so I won't be too easy to scout. But, I have no idea how successful my plays are, or how many times I run a certain play, because I have NO confidence in the accuracy of the numbers displayed in the play selection screens.
I have been pretty successful without ever trying to limit my plays, or even have a rule to run a specific play (or formation), other than in some leagues I have a rule to always run it on 1st and goal from the 2 or less.
My point is that you can win in MFN and still have a good variety of plays on both offense and defense. You don't have to blitz all the time (I probably blitz less than most), and you don't have to limit your offense to just a few plays.
You make it sound like there is only one way to be competitive, which if your posts are an indication of what you think that way is, I am proof it is not true.
You can find plays and players that will work for you and build your team into a perennial contender while still having the type of team you want to have, but it doesn't come overnight.
Be patient.