An example of why it's important to go to higher sensor pixel counts is the aliasing that occurs with modern lenses on 45 MP FX sensors; when photographing small birds with the D850 and 500 PF, I've experienced a lot of moire. In my people photography I typically avoid the issue by using faster lenses at wider apertures (such as f/1.4-f/2) or deeply stopped down (in the studio, f/11) where the moire is rarely exhibited, but at mid apertures it's a more frequent issue. To avoid it and to extract maximum (true) detail out of a lens, the sensor should be clearly higher resolution than the lens. Otherwise the issue will pop up at optimum aperture with proper technique (either electronic or electronic front curtain shutter, tripod, fast enough shutter speed or flash). As you increase sensor resolution, when there is no longer any change in the image at optimum aperture, then the sensor is high enough resolution to get correct rendering of the subject. We are far away from that with 45 MP, and lenses keep getting sharper and sharper so the goalpost of aliasing-free imaging keeps being moved (and higher pixel counts will eventually be needed to resolve the issue).