I think they've missed the point. Venting isn't for catharsis; It's for seeking validation. When you vent TO someone and they lend a sympathetic ear, it's a huge help. Venting is a social bonding ritual. You generally don't get this online because most of the audience is NOT sympathetic, so you'll get criticism after criticism, making things even worse.
You'd still vent, if alone on a desert island, maybe to The Gods.
Ever hear yourself saying out loud, usually with expletives, something that you would "never say"? Listen to that voice!
That's communication of unconscious but frustrated thoughts. Sometimes it has to come out verbally because ones inner dialogue isn't strong enough due to social or superego suppression.
After you said it to yourself you feel better.
We are not the singular identities simpler minds suppose us.