You're wrong, it can often be a bad thing.
Trying to be the catch-all console focusing in equal amounts on handheld and console gaming has a lot of potential to lead to a 'jack of all trades, master of none' situation where the focus of the device is divided and neither side gets the attention it deserves. You'd end up with a crummy handheld that's trying way too hard to be a home console and vice-versa.
Sure, in a purely theoretical scenario it's always good to add every feature and option you possibly can. But everything comes at a price. Shipping with motion controllers makes the device both more expensive and less portable. The motion controllers likely won't get utilized for handheld gaming either, and it puts developers once again in the position to decide whether to divide their attention and support that input or cast it aside completely, making it a waste. (see the Wii-U screen for an example).
So no, I believe it is more beneficial to either side to have one control scheme that applies to both the handheld and the console setup. And i'm convinced that Nintendo is served better by going all-in on handheld with some docking features than the other way around.