There are some shocking subs out there but, on balance, I would say a sub is a writer's friend.
The best work with a writer to coax cogent work out of the most dodgy raw material, spot literals, correct grammar and generally stop the wordsmith looking like an arse.
I once had a row about the phrase, 'another day, another dolour'. I didn't think it worked and told the writer so. He wasn't pleased and later tried to lead me into a broom cupboard for a fight.
This remarkable tirade
from Giles Coren is no way to make friends.