Sorry, these were on the other page, but I just wanted to point out that it's not true. Don't worry about this.
Your rank is based off of several factors: time taken, BP, longest combo, zandatsu, and kills. Maximum score for each component is 1000 points, and you need 5000 to get an S Rank. If you take no damage, you will get an additional 1000 bonus.
Though you can get some extra BP from blade mode like cutting off limbs, I'm certain you can get BP from other things like stylish play.
The scoring system is set up that you can leave out a component entirely if you like, too. If you just want to play with your food, you can sacrifice the time component, but you have to be smart about it. If you're a good player who doesn't want to bother with Zandatsu finishers on everything, you don't have to. The combo timer is also really generous, and sometimes you can use psychotic blade mode slashing to pump up that counter. Many powerful attacks encourage blade mode afterward (the action freezes for a second), so it's interesting to see how each aspect of combat feeds into one another.
It's not perfect, but I'm starting to understand the reasoning behind it. A Gekko's grapple does no damage, for example, but it's there to screw up your combo counter. Also, the dizzy system and parry counter system let you go from enemy to enemy for better battlefield management if you don't want to kill things one by one. This is also how ninja run is incorporated into fights: you can automatically leap over stunned/crouched enemies like an obstacle, the wide attack while running lets you slash on the way to your destination (likely to maintain combo counter and/or to interrupt foes), and the strong attack slide and dive kick let you close in on things faster (the latter being viable because of air parry). I'm sure this is also the reason why we have an unlimited wide attack combo. Strong attacks probably cause more dizzy stun, and the breakdance is useful for when you're surrounded. The same goes with the invincible jump+wide attack sidesteps and backsteps--you won't be caught in parry block animations or forced into the parry counter that leaves you vulnerable. Lots of interesting situational stuff like that, imo.