You're correct of course and I understand this. I quoted moneysavingexpert hoping people could look at the article themselves to make an informed choice.
The nub of it is that unit prices are rocketing in current fixed tariffs being offered to existing users so delaying fixing COULD be costly, especially if there are no exit fees in what's being offered.
I've been careful to include 'worth considering' in what I've written. The ''best guess as a rule of thumb'' on that site is now, ''If you're offered a year's fix at no more than 95% above your current price-capped tariff, or 100% more if you very strongly value budgeting certainty, IT'S WORTH CONSIDERING''. (Capital letters inserted by me for clarity).
Just trying to help by flagging-up the information I'm finding but of course it's every individual's choice as to what looks best to them.