As far as I understand, the "problem" was that they gave Monolith too much time.
Anyway, you're right that they should have done a lot more to market the title, as the sales really didn't reflect the ratings at all - highest rated JRPG in years, maybe even the highest rated JRPG of all time. Globally. On the other hand, the shout out at the Wii U Presentation gave me hope. Xenoblade was probably considered a test, the results were probably far better than expected, and the team reached a point where their next project is basically mentioned in one sentence with the next Smash Bros. That's
huge - and well deserved. And it's another thing I love about Nintendo recently: They put the creators in the spotlight. Not just IPs or studios, but the actual people behind the titles.