I think the PSP would be doing better if Nintendo never released the DS, but I still don't think it would be doing extremely well and would probably remain in second place to the GBA.
Most of the reasons the PSP continues to be in second place have to do with its games and features. The system's design and games aren't very portable friendly and the PSP mainly sells to 'hardcore' users. Nintendo's years of experience and understanding of the portable market have made their line of portable systems the one to beat. Sadly, Sony didn't take those lessons to heart when designing the PSP.
Numbers are like people. Torture them enough and you can get them to say anything you want.
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