It sure is, if you are using Windows. Because Windows scales fonts so inconsistently, to avoid eyestrain most people are going to want 80-90ppi pixel size so the smallest system fonts will still be easily legible--even when things don't magnify properly when fonts are set to 150% size.
100ppi is a touch too fine but barely readable with some eyestrain, so with 1080p 23.5" you can read everything easily while 21.5" would require some straining on the smallest text, especially for older folks who should probably even drop to 80ppi.
I understand Mac has no such issues with font scaling so small 4k to 6k screens are just fine there