I think the idea of brake in is to "eat up" the piston to the point where it will move freely into the tapered sleeve and expand the sleeve so it also matches the piston.
I suppose the reason not to hurry it up is not to destroy the surfaces of the two parts.You want them as smooth as possible so that you don't have leak down at the compression stroke.
Those who destroy their engines at break in maybe is because they rushed it and cause it was too close they destroied the piston and sleeve.Think about it!!!

So bench or no bench, an engine that revs too much at brake in will be !

I also believe that an engine should be reved with some load on it like an 1:1 engine would be broken in.