I think Buddy Hall is breaking well, in the video, without the use of extra muscle force, because he is employing BALANCE for power. Plus his BALANCE affords him very good accuracy of hit..
In the video, Buddy Hall doesn't display a posture that would say, "my lead foot is out there 6 inches further than I like", but it does say "I am comfortable & I have my balance".
In every human movement, BALANCE is emphasized, over & over, for control of one's actions, for power & accuracy.
The "MAGIC" of the Break Shot, for a well racked 9-Ball Rack, racked close to perfect, can be discovered by methodically racking the balls & firing WHITEY into the RACK, from a pre-determined location (24-27 inches away). Always use a reference point (Golf Tee on the back Rail) for your shot Line.
If your original attempt doesn't work, move the TEE a 1/4 inch to the left or right, until things start to work for you. If you can't get the movement of the TEE location, to work, you have to allow the TEE to remain in a permanent location & move the Cue Ball location, a 1/4 inch to the right or left, for a successful Break Shot.
We have all witnessed many top players make a wing ball or the lead ball or the back ball, on the the Break Shot, time after time. That isn't magic, the knowledge is the MAGIC.