While I don't disagree with the overall premise of your OP, the series that you give as an example aren't that good, since both have had great and substantial releases on home consoles whose quality has not dwindled and have prospects of releasing games in the future for home consoles as well, keeping on par with the previous games in terms of quality (DQX comes to mind).
Handheld releases doesn't equal instant quality (see Tales of series, their highest quality games are on home consoles, not handhelds). It has all to do with how well developed the games are, no matter in which device they're in.
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