KDE Plasma has currently better upstream development (a side effect of Steam Deck) but the integration of KDE into Fedora is done by volunteers.
Gnome is integrated into Fedora by Red Hat employees but upstream development lags a bit behind in adopting some newer technologies Red Hat isn’t that interested for RHEL.
I used Fedora in the past and found the KDE Spin a little less polished. I don’t know the current situation but there was a time Fedora KDE shipped out of the box with three web browsers because the volunteers couldn’t agree on one, whereas the RH employees just decided that they want Firefox and not Gnome Web for RHEL, so in Fedora they just did the same. Updates were rolled out in a timely manner (and I heard nothing that indicated anything changed in that regard), so the volunteer squad didn’t do a worse job there than the paid Gnome people.