So a basic design saves on maintainence but is it at the expense of flipper power is what I want to know.... ??

Is a Stern flipper as strong as a B/W or other technically, and if so , or not , why technically ??

I think it comes down to regular maintenance.  Look at the speed of machines like ACDC straight out of the box.  The coil power can be turned down from memory but nothing beats regular cleaning of the playfield, balls and trough as others have mentioned plus the flipper rubbers play a big part as well.  Fresh rubbers make a world of difference as well.  Even if the rubber is rotated around the flipper bat, if they are too stingey to replace the rubber, will help.  You can get two or three cycles out of the rubber this way.  Even just cleaning the flipper rubber will help a little to get rid of the black crap which becomes almost sticky and reduces bounce off the rubber.

Keeping the flipper plunger clean and coil sleeve will assist as well.