He gets battered because he regularly presents conjecture as definitive fact. It's not just Witsel and Mata from 2016. It was also his adamant insistence that Usmanov would never sell his shares in Arsenal to Kroenke. And just last month we had his pronouncement that Kenwright would be gone "by Wednesday" when there wasn't a shred of evidence to suggest that would be the case.
He positions himself as an authority - blogs, podcasts, definitive tweets - when he's merely speculating.
I quite enjoy him. His takes on the financial side are worth listening to. But beyond that you might as well be reading Alan Nixon...