Strength, speed. and size are physical attributes in the martial arts, and as the martial arts are physical one should cultivate these as best as possible.
Take stock of where you are in the moment, and work through flexibility, strength training and conditioning to improve a bit each week.
They are important in the martial arts, and a part of training, but are they the *martial arts*?
One can not control the strength, speed, and size of your training partner, let alone outside of the dojo.
Utilizing martial arts skills based on this is a literal gamble.
Are you bigger and stronger?
That is why the martial arts focus on distance, timing, balance, and rhythm. Attributes of waza (techniques) that can be controlled regardless of the situation.
That is why self-defense, goshinjutsu needs to rely on no power.