Since kata has it's foundation in kihons(basics), doing kata should have the same effect as drilling your punches.
i.e. You develop muscle memory doing the kata over and over again.
With muscle memory you get faster, and your strikes get stronger as well. You can consider sparring, striking the makiwara, bag work, etc. as supplementary training but I believe everything can be derived from kata, especially generation of power.
hope this helps, good luck on your training.