As you have Horizontal progress and Vertical progress, true innovation is most likely both.
It is incredibly difficult, if not impossible, to create something completely new without relying on something else.
One could say that Twitch, the video streaming platform, was both horizontal and vertical. Horizontal in the way that streaming video’s existed and video platforms like YouTube were already dominating the internet. Yet it was vertical in a way that it was a new market to focus on video game streams and build a whole platform around streaming.