The makiwara is to train karate-ka to break boards, bricks, ice blocks, etc. for demonstrations?

Again, caveat: I speak only from my perspective. :-)

No, an emphatic no. I cannot speak more about this than say no, no way, no how. The makiwara tool is useful in many ways and it may be generally viewed this way but it is not and was never meant to train karate-ka to break things.

Tameshiwara is an art form all unto itself and does use the makiwara training tool to enhance the ability to perform the art of tameshiwara but ...