OP, in the end, this isn't a consultation for parents and students. Working this all out is a highly technical and statistical process. It really isn't something that parental or student comment is useful for. Schools will probably put forward one set of considered opinions, rather than all teachers expressing random (and not so useful views).
People forget that every year, when exams are sat, huge amounts of statistical adjustment goes into determining results. It really isn't simply that by working hard the grade is determined. Prior attainment of the cohort (via GCSE or SATs - using data which they have across a huge cohort, rather than worrying about the fact some individuals don't have that data) is always relevant and boundaries are adjusted for difficulty of paper and subject and to ensure similar percentages over time or that reflect the ability of a cohort, to try to give grades meaningful parity over time. It is very involved.
It is true that exams are fraught with problems. Never mind the whole issue of the sense of luck in some questions, but also the scope for error or a range of interpretations in many subjects, the fact examiners are laid little and have to mark too many papers etc all mean that vast numbers of papers are incorrectly marked and only some ever go to re-mark.
I'd think this process will deliver as accurate if not more accurate results for the vast majority. The trouble is that people won't see it like that. Anyone who is a bit disappointed (and over 75% of grades are below the UCAS prediction) will decide that they were cheated by this year's system....not realising that if they had sat the exam, they would dry likely have been disappointed trouble is parents and students won't see this. They will decide that the teachers gave them a low grade because they hadn't slaved for their mocks, when they planned a heroic effort of revision in the last weeks but were denied the chance to do it, or that SATs which didn't reflect their true potential were relied on, or that the school not being a top performing school made the system prejudiced against them. People won't just say 'that's what they deserved' because they usually don't really know what is most likely and because the system this year is different.
Unfortunately there won't be any way to overcome parental and student determination to believe that they have been somehow cheated out of higher grades this year. The complexities if the system will be too difficult to understand and huge numbers will be convinced their child was on the verge of a massive breakthrough but were denied the chance to shine. Most won't go for an autumn exam, because even if a bit disappointed, most will be able to move onto the next stage, as they always do even when a bit disappointed. However, those who go for the autumn exam, will often be disappointed in not performing better and then feel aggrieved about the whole thing of being out of school for so long before the exam. There will no winning for those running this.
Usually when people are disappointed in their results, they feel at least some responsibility for it, due to sitting the exams. I think the results will be extremely similar to they would have been with exams, but sadly the sense of being responsible will be lost. Hopefully, the annoyance and disappointment will be short-lived and and not a malingering bitterness which results in lots of late exam sitting and dwelling on the seeming unfairness of it all.
The government wants students to be able to move onto the next stage...and the vast majority, as every year will find the grades this system gives them, allows them to do just that.