Some of the hardest games out there is enjoyable in short bursts. What has time it take to play a game with casual or hardcore?
If time was the deciding factor tons of games would be inherent casual on all platforms.
True, But Breath of the Wild and Mario Odyssey are very forgiving in difficulty. Yeah, Breath of the Wild is challenging, but it's never brutally hard thanks to frequent autosaves, which means your given a fair chance to learn from your mistakes and conduct a better approach, or simply do something else since there's plenty to do in the game.
For Mario Odyssey, Game Overs and lives have been stripped out entirely, so even if you die, the worst penalty is that you loose Coins, which you can easily earn back anyway. Plus, the game even includes an assist mode that literally points you to where you should be going, as well as prevent death from falling. And like BotW, there's also frequent autosaves and checkpoints.
There's a misconception that casual gamers don't like being challenged at all, which is untrue. Any gamer be it casual or hardcore, likely enjoys some form of challenge every now and again. Breath of the Wild and Mario Odyssey are challenging games, but they're also very accessible games, even to those put off by console games.
I think the way you are using the term 'casual gamer' is different than how most would interpret it, and that is leading to some confusion.
If you are saying that Nintendo is trying to accommodate players who can't fit long play sessions into their lives, then it's hard to disagree with that. If you are suggesting that Nintendo are going for the Candy Crush crowd (what people understand casual gamers to be), then you couldn't be more wrong.
Both really. Part of the reason mobile gaming became so huge is because people's lives are very busy these days. They don't have time to set aside to sit in front of a TV for hours and play video games. Smartphone games took off because they were simple, accessible games that can be played in bite sized chunks, so people who like games, but don't have time for something like Dark Souls can enjoy them with ease. Gaming on phones is so ubiquitous these days that it's become the new default entry point for non-gamers and new comers to the medium. Plus, they're on a device people already carry with them.
With the Switch, Nintendo's goal is to simplify home console games, to fit the lives of the casual gamers who play games on their phones. It may just be my interpretation, even Nintendo sort of admits this when they describe their smartphone strategy. The Switch isn't meant to replace your phone, but it is designed to accommodate those who are used to mobile gaming.