For me part of the problem is you lose contrast. The color contrast is no longer there, so colors that are a similar brightness but different hue turn a similar shade of your chosen color. Plus whites get toned down significantly by tinting, so you lose brightness and contrast there too
I think they need to leave white as white instead of tinting it, and increase the contrast when doing the conversion. The color part will need to be fixed by devs submitting different icons.
Also the icon background should honestly be what gets colorized, not the icon itself. If I want pink icons I’d rather have a white let’s say Apple Music logo, over a pink background, that would be aesthetically very nice