A pretty fair assessment in my view, Mitchell Davey isn't good enough and like Grondal who clearly wasn't good enough either will no doubt will be replaced, Zach is a improving rider who had bad luck with injuries last season but as you say should be at number 7. Bellego has ability and it was reported he had equipment issues could maintain his average but I think that is unlikely and could drop back a bit to something like 6.5, Musielak is a top rider and could easily maintain his average or up it slightly and Ellis could put at least a point on his average. Batch is Batch and we all know what we are going to get, he can be amazing like the time I remember him guesting for Poole against Wolves and winning a vital heat 15 but that kind of form doesn't happen often enough.
The top five has a solid look about it but you need one good reserve and in my opinion it is not fair on Zach to be that rider, he is going to need to win a lot of reserve races.