First of all, anyone with any loft, is muscling the ball. Because, they're squeezing and/or hitting up on the ball, using muscle to loft it out there on the lane. So, anyone whose ball lands at the dots or beyond, is muscling the ball. That's over 50% of the bowlers, maybe more.
In a perfect pendulum swing, there will be only 1 speed. If you lifted the ball to the height of your backswing and just let it fall, I'm not sure what the exact ball speed going down the lane would be, but it wouldn't be very fast. Yes, you can increase speed to some degree with a faster approach, but I doubt very much, with a perfect pendulum swing/free armswing, that the ball speed would be much more than 16 mph.
In order to get a higher speed, especially ones approaching 20 (most of the pro's 18-20 mph) one has to be "pulling the ball through" on the downswing. This is muscling the ball.
If you have a high rev rate, over 400 rpms, then there's no way you can not muscle the ball, without the ball hooking too much on most of todays conditions.
So, if you really want to have a truly free armswing today, you better be a fudger..!! I stand by my original statement/s..!! =:^D