Restoring the royal prerogative for calling elections transfers power from parliament to a prime minister who cannot be trusted to wield it honourably
Two primary checks on a British prime minister are parliament and character. The country’s highest executive office is restrained by the legislature; the incumbent’s actions are, ideally, conditioned by natural decency.
Neither has much bearing on Boris Johnson. His party has an 80-seat majority in the Commons, which means he can mostly enact legislation of his choosing. Even his friends recognise that probity and self-restraint are not dominant features of his temperament.