Tony Benn's problem was that he never engaged with the real world. He, quite rightly, railed against the media's habit of measuring issues by volume not merit. That is, the way reports on a protest focus on the number taking part but ignore the speeches.
He didn't, however, realise that he needed to adapt if he wanted to be heard. He expected the media to cover an hour or more of speeches in full.
I'm not saying he should have gone down the facile sound-bite route that many politicians do but I don't think I ever heard him say anything that didn't include a reference to some person or event that only a politics graduate would understand.
If he'd found a way to convey his message in forty seconds rather than forty minutes he'd have been much more important.