Big parts of Monolithsoft having been busy with Zelda doesn't mean that Xenoblade 2 was developed by a B team. People seriously need to stop giving teams names like that -- as if anyone at Monolith was thinking: "Oh yeah, we give Xenoblade 2 to our lesser staff while we work on Zelda". Classifying teams like that is silly and frankly insulting.
Apart of that, I was always expecting Xenoblade 2 to be developed by a smaller team considering Monolith's involvement with BotW seems to have been quite extensive. I was expecting Xenoblade 2 to be a smaller game due to that -- and I was honestly surprised when it wasn't. They did great work handling two big projects side by side.
Monolith Tokyo (the main studio) wasn't involved with the production of Mario Kart, was it? I think Zelda was the only time Monolith's development studio helped on the production of a Nintendo project to a significant degree. Monolith Kyoto, on the other hand, was founded to support Nintendo's internal teams and has helped with a lot of games (they are mostly just creating assets though, they don't seem to have more than a couple of programmers if at all).