Generally, you'll always have a better chance of success producing an App already in demand, independent of market share any company holds.

Consider the Apple II, Apple screwed over their customers and lost a suspected 80% market share + came very close to bankruptcy.

The IBM PC... well... IBM stopped manufacturing this hardware around 1982 after they went from 100% market share to around 18% + could no longer make a profit.

And my all time favorite Microsoft's destruction of the Skype product. They got so many complaints about Skype 8 that they locked the complaint thread after 48 hours.

Skype went from nearly 100% market share to spawning so many competitors Skype will likely go the way of the carburetor, buggy whip, 8 track cassette shortly.