Brake lines that when they come off the Master cylinder

Yes I understand perfectly. Problem is from a mechanic he said the braided
parts need to be ordered from the dealer. Another thing he said was it is difficult
to remove the fittings off the master cylinder and if they strip the whole thing needs
to be replaced at a cost of $1800 (master cylinder).
Other things are wrong with the car, like catalytic converter, oxygen
sensor. Just want to get rid of car at this point as it is spending a lot
of time in garage.
Why do they use a braided line then? This is a known defect and I read
elsewhere a few years later they replaced the braided section
with a hard line. They never admitted the design caused corrosion
and brake failure. There have been formal complaints on this issue.

But the brake line ATTACHED or welded to the braided line corrodes due to dissimilar metals used. I can show you pictures from my wife's car. Yes I know it's safer to use factory parts.