If we did simply go by teacher assessment (for one year only), would it be such a bad thing?
Those who would have done better in the exam than the algorithm thought will get what they deserve. Others will get more than they deserve - it may open a door through which they will stride purposefully onto a path leading to the sunlit uplands (other metaphors are available) - a potential realised. Or it may be a step too far and they stumble but then, hopefully, find a better path for them.
In one of my A-Level subjects, the entire cohort did worse than the mock exams had predicted - those expected to pass well, scraped through; those expected to pass so-so, failed; no one got better than grade E. I was saved by the fact that, aged 11, I had chosen a scarcity subject where the universities couldn't be picky. It was a very lucky break.
Sometimes people get lucky breaks. Mostly it's the children of the rich and powerful; it would be nice if sometimes it's other people.
As I've mentioned in a previous post, many universities over offer on places as they know a certain proportion won't get the grades. If everyone got the predicted grades, they suddenly have more students than they have places. There's a numbers cap in place, so even if they could find the resources to run the course for everyone, they're probably not allowed to.
Conversely those universities that don't over-offer and rely on making up their numbers through clearing are facing a shortfall which could be quite serious on their finances.
If you were going to decide to use predicted grades after abandoning exams, that decision needed to have been much earlier in the year so the universities could adjust the criteria they use to make the offers on. (Oxbridge make their offers in January, so that ship had long sailed).