Before RTO systems was always taught heels on the floor
There are probably thousands of unreported occasions where a pilot had inadvertently touched the top of the brake pedals during the take off roll. Sometimes more prevalent with someone with big feet or having his seat too far forward and thus cramping leg movement. Or maybe deliberately choosing to have his toes resting on top of the rudder pedals "just in case" he needs to instantaneously stop during the take off run. In a similar vein, there are pilots who when their hand is on the thrust levers during a take off roll, deliberately bend their hand like a bird's claw over the top of the throttles as if to signify he is poised and ready to rip the throttles back in an instant should something untoward happen. I found that having one's feet high up on the pedals during take off roll or landing means my ankle is at an uncomfortable angle and feels unnatural.
Keep in mind it takes a fraction of a second to move one's toes when required, from their comfortable position at the base of the rudder pedal, to the max braking position at the top of the pedal. During elementary flying training in Cessna singles most pilots were taught to taxi, take off and land, with feet at the bottom of the pedals. Reason why? To avoid inadvertent dragging of the brakes. Why any different with airline aircraft?. .
Early aircraft with rudder bars and no toe brakes usually have mechanical brake levers and use differential directional braking by pushing one rudder pedal and gently squeezing or pulling back on the brake lever. Yet I have never seen a pilot on these types (Chipmunk for example) taking off with one hand wrapped around the brake lever ready for instant action if an abort happens.
The early Boeing 737-100/200 FCTM displayed a diagram showing the takeoff and landing technique of having the feet high up on the pedal but with toes bent back just clear of the top of the rudder pedal. It was damnably uncomfortable but showed how instant brakes could be applied if needed. Later issues of the FCTM had this diagram removed. Maybe for a good reason based upon how easy it was to inadvertently apply brake pressure without being aware of it?