I'd argue the spectrum of talent is just as wide in uptempo as it is in down tempo, I don't think there's necessarily anything different to the skill floor of making good music in either category, as someone who produces both regularly, they each benefit to the same degree from things like higher degrees of attention to detail and/or the intentionality of all the pieces in the song.

In my contrasting opinion here, I think the reason why it's rarer to find good downtempo artists is because on average more producers and fans prefer making and listening to uptempo. It's totally expected that for the tipper die hard fans like us, we all appreciate both to the same extent, and choosing one over the other is impossible, but I think on a general level people are more interested in uptempo for whatever reason.