Bachus, I think accordion was perfect to learn keyboard..
By design you have circle of 4ths going down and circle of 5ths going up on the bass buttons..
All accordion students learn theory, I cannot say the same for typical piano students..
Also accordion players have a strong foundation to play chords and understand the voicings and intervals... Piano students not so much..

I also believe that accordion students can adapt to left hand bass easier than piano students..

Both develop strong reading skills.. with slightly different bass cleft side of things..

BTW: some of the best all around keyboard players I know are mostly trained accordionist..

I would say the top three players I know are accordion players first, and excel on keyboard, organ, and piano too