Minecraft was done by a lone dev. Generally, I think it is the opposite, a lone dev works faster than a big team. Why it is that is a mystery of the universe but that's how it works to my observations
you, as a lone developer will always be late.
As for people being tired of cubes, it's the same question about people being bored of pixels. It's an elemental block of which you make a game, it's too small to really get bored about since it alone does not decide if a game will be fun or not.
If this is about "cubes that work like Minecraft" then it is another thing of course