SPI screen slow drawing question

[iamisti]

According to the documentation SPI screen drawing is very slow. But I found a video where someone uses the same connection with an arduino board and he gets solid fps rates.
Can you explain me why SPI update of this library is very very slow? Where is the bottleneck (in theory there should be no bottleneck)?

Here is the video:
https://www.youtube.com/watch?v=sFGsYZ0Hszk

Also this one:
https://www.youtube.com/watch?v=xI6dXTA02UQ