Its kind of necessary for xbows because they have no other requirements. You get 14% chance of repairs per minute with 1wpf I think, and yet you can still hit things with 1WPF.
I would rather it had better diminishing effects and started very high, like <50 in proficiency = 80% repair chance, 50-100= 50%, 100+= 4% (but it would be on a curve and get quite low at around 100)
If not that then 3x melee should have some code that reduces repair chance based on how much WPF you have spent in total