If you play bayonetta on pc with a keyboard/mouse or controller, here's an easy way to win the button mashing sequences.
All you need to do is set two buttons for one action "set 2 buttons for punch, two for kick, and two for shoot". When the sequence starts "torture attack, QTE, boss fights.....etc" when you need to mash buttons, use both buttons of the required action. You will fill that button mash meter in much less time/effort.
Example: I play with xbox one controller connected to my PC. Shooting is mapped to X on the controller, and to E on the keyboard by default. When any sequence that requires mashing X starts, I quickly place my left hand on the keyboard and start mashing E, and with my right hand I'm mashing X on the controller at the same time. I win very quickly with much less effort, and I manage to overfill the meter and gain more bonus points in the end.
Example 2: The game allows you to map 2 keyboard buttons to each action. You can change the mapping from the options, and map F for kicks as an alternative "LMB is the default". When you start a sequence that requires mashing kick, use both LMB and F at the same time.