You're comparing Atari to Amiga not Commodore? And then you say that Atari have been there longer? You're not seriously saying that 8 bit Ataris have anything in common with their ST successors, are you? Just because they were called Atari doesn't make them one family.
In your logic all predecessors to the Amiga from Commodore should also count; the C64, Vic20, PET etc. They're from the same company. Heck, Commodore was founded in 1954. Does that make them the winner?