Correct, Gary wrote pretty much all of the Take That music from the very beginning, he's very talented as well as being able to play the piano. The band was built around him. Unlike other manufactured boy bands who were put together and had less creative control, although to be fair to One Direction and Boyzone they did have input in to their songs, but nowhere near the level of Gary.
You often find that once the band is up and running and they become bigger then you start to see in later albums they assert more control of the songwriting, as that's where the mega bucks are.