I wish we had the previous system of being able to appeal in person to a panel in January
You are not alone!
If the review fails then subsequently appealing seems pointless, unless you can prove the review was unfair in some way.
Not necessarily - in other authorities that have this system, appeal panels have been known to take the initiative, ask awkward questions, and decide that they were not satisfied.
Is it true (as I think I read somewhere here) that the review panel will not consider his class teacher's letter of support ......... ?
I don't think so. What I think you've seen is an attempt to stop both the headteacher and
class teacher being asked by everyone as a matter of routine to provide support, thereby creating extra work for the school (and the possibility of contradictory opinions!).
I see no reason why you shouldn't ask the class teacher - to see what the response is.
At worst, it will be "Sorry, it's against school policy." At best, you'll get the letter!
Any relevant evidence (other than school work) ought to be considered by the panel.