I don't see why having 100% would be a problem as long as they are limited to 1 or 2 people in the game and not one in every settlement you go to. Some people are experts or even masters in their field so why can't there be none in repair? It's only more realistic to have repair experts.....some are just better than others. However, it shouldn't be cheap to get your weapons fixed by these people and it should cost at least 2500 or 3000 caps (minimum).
1 or 2 tops- and given the number of factions and the general "faction against faction" situation, it would make perfect sense from any angle that they would be in the service of some big army-fielding faction. Maybe by choice, or just as possible: the faction's got an army to equip, and has conscripted whoever they need by whatever means necessary.
This could lead to all sorts of scenarios:
You have to be in, and in
good, with that faction to have access- and even then you're regarded as "taking time away from" their "aiding the war effort" so you get charged out the wazoo.
They're enslaved/conscripted and manage to escape- you're sent to retrieve'em, and after dragging them back kicking and screaming they're none too happy about working on
your gear. So they give their captors a hard time to the tune "I'll fix
yours but that weasel who dragged me back?", and the captors play along with it to try and get their own side's stuff taken care of with as little fuss as possible.
At best, access to 100% repair ability should be "significantly less than easy" by any means other than the self-reliance method of building your own skill up, is my view on it.