I'm sorry to say but your are making one of engineering rookie mistakes. Much like the example of where the sailors blows in his own sail to propel him along.

The spinnaker does definately pull upwards at the end of the pole. However it very much pulls downward at the mast hound fitting. As the mast adn spi pole are fixed relatively to eachother this means that these forces will largely level eachother out.

This is called systems thinking in engineering. You must learn to regard a fix composition of elements as one whole system where internal forces have no meaning when looking at relations (newtons laws) that are taking over the whole (system)

Wouter