Yeah, the idea that a printed map is necessarily going to have more accurate routes than something you find online is sort of laughable. In fact the opposite seems sort of likely: if a route changes or goes out of date, you'd expect an online source to get updated before the maps you can purchase in a store (if you even think to repurchase a map as opposed to using the one you bought 3 years ago).

But I don't know that I'd agree that the issue is that the app is designed for driving, not hiking. I've had similar issues on supposedly drive-able routes. On a recent trip Google Maps tried to take me down many roads that were various combinations of non-existent / closed / dangerous / impassible. This was in California. We're talking barely a hundred miles from Google's corporate headquarters.

So yeah, it doesn't surprise me at all that certain remote areas don't have accurate / sometimes have dangerous routes shown on the map. Accuracy is hard, you really need local expertise. If you're going to a park or established wilderness area, the managers should be able to provide you with up to date information before you go. That's the only kind of paper map you should be trusting.