In most LA's there are schools the LA can more easily strong arm which might explain this.
Also this may be to do with your right to a mainstream education, but not a specific mainstream school.
At tribunal they will first look at whether one of the following apply. - The setting is unsuitable for the age, ability, aptitude or special educational needs (“SEN”) of the child or young person; or
- The attendance of the child or young person would be incompatible with the provision of efficient education for others; or
- The attendance of the child or young person would be incompatible with the efficient use of resources.
These are the only reasons your preference can be refused. If none apply your preference will be named.
If one does apply the type of placement will be considered i.e. Is MS incompatible with the efficient education of others and are there no reasonable steps to prevent the incompatibility? If no, mainstream will be named as the type of placement and the tribunal will consider all the schools put forward by you and the LA. The more schools the LA put forward the more chance the Tribunal will find one it deems suitable.
I would pressurise the LA to name your preferred school despite their reply to the consultation, which they can, and should, do unless one of the 3 reasons above is applicable. On its own the school believing MS is necessary isn't enough to refuse admission and the LA will have additional transport costs for schools further away.
An alternative route is making noises about expensive independent schools, you may find someone is pressurised into has a change of heart. Alongside this ask what the LA's plan is for providing for an education and the provision in section F in September as they are still responsible for ensuring provision is provided.
Have you asked for an expedited hearing?