I would put the worst misstep down to how they dealt with the internet in the early days. That's not to say I think Sony or Microsoft did particularly well out of the gate, but Nintendo seems to have started by ignoring it, then pretending it didn't really matter, to suddenly embracing it but only halfway with limited online functionality compared to everyone else at that stage, to then having a huge amount of friction with content creators.
It just feels like as a company they don't know what to do with the internet and at this stage of the game most companies have integrated internet services/engagement that isn't perfect but is typically functional. I wouldn't see anything wrong with Nintendo basically saying "we use the internet to distribute digital games, and we have certain specific games that allow multiplayer, and that's it", but they seem insistent on keeping up with the Joneses in spite of not really having a plan or a will to follow through with a lot of stuff.