The triplet is not sharper in itself, just likely better color corrected than said doublet.
A substantial role in this price category is played by sample variation, but generally, the larger doublet has an edge in showing planetary or deep sky detail visually. Photographically, the better color correction in the comparison between these two instruments gives the nudge to the smaller triplet.
Another consideration is the stability of the mount you have or intend to buy. The 5" has a shorter moment arm than the 6".
Local seeing conditions and the thermal situation are another important factor. Is there a larger or smaller temperature difference where you observe? IS local seeing good enough to let the bigger 6" shine?
And lastly, which instrument do you subjectively like the most?
Good luck in choosing. And especially gettin the instrument physically in your hands in these very challenging times globally, both effecting production and transport of instruments.