I never have much trouble with leather dulling knives unless sheath too tight and edge cutting the welt.

Spyderco uses Boltaron now, and it supposedly not as bad as for dulling. But any flat grind plus plastic sheath pinched shut at edge means the edge drags on plastic.

Knives with thicker primary grind at edging and pronounced secondary giving shoulders which keep sharpened edge off plastic will help a lot.

Plastic is quite bad as to having grit embed in the surface and no cure for that.

And entire point of the plastic sheaths are ease of manufacture, cheap, and proof against environment.

Doubt you will see anyone do anything to cut into profit margins, not even added a (wonder of wonders, what a novel idea) welt to a sheath edge, not even of plastic.