You're right, those are problems. But they're not problems with this law, they're problems with jury-based criminal justice systems. And the system's had 900 years to evolve solutions -- judges summing up, "No case to answer" / directed verdicts, etc.
There's room for disagreement about how effective those solutions are. Point is, as the main objection to this law, that complaint 'proves too much' -- since essentially the same objections apply to all but the most trivial criminal offences, the solution then becomes scrap juries and go for a Germany-style professional/inquisitorial justice system. (And maybe we should, I don't know).
(btw, this is very, very far from being the most complicated law or subject matter that juries have to face, compared to e.g. complex fraud trials)
(To be clear, I think this is a terrible law! But just because I agree with TFA's conclusions doesn't justify his fearmongering, IMO)