Leeds got to the Champions League semi final with Harte as an important member of their squad. Your argument of "they'd no-one else" is laughable. Sure, I'll make myself available the next time there's an injury crisis for us and if I've a nightmare then I'll be able to say "sure, they'd no-one else but me!".
If he was that bad, managers would have played anyone but him at left back.When Harte was prominent for Leeds it was during their silly money stage. I'm sure they would have bought an able replacement if they had no faith whatsoever in him.
As I've said, you don't get to pick up all that experiance by being a bad player. That for me nails it.