What is the weakest cover using the Mastermind core?

I would guess the scholar.

Have to say Scholar. Mine needed lots of friction to work well.

If you are talking about overall hook, then the Scholar would be the weakest.

I am asking in terms of required oil. 

My opinion would be that the Scholar would be best on drier conditions, especially at the factory finish.  Great length through the heads.

Having said that, once the ball finds friction it's pretty strong.  It will allow you to open up angles as the lanes open up for you.  Even more so if you'll break the surface on it.

Nailed it

The Brainiac excels as and after the lanes transition, and that's what Brunswick targeted with that cover.  On the fresh the Einstein is great, with the Scholar, at least for me, is a small move closer to friction.

We all bowl on varying conditions and lane surfaces, so each of us may have slightly different experiences.

>> What is the weakest cover using the Mastermind core?

The one made in Mexico.