The 'vision and values' are largely set by the prejudiced views of the sponsor not from any basis in evidence of what works best in education.
Yep, agree, there's a lot of responsibility on the decision makers - i.e. the Secretary of State and her delegates (the regional school commissioners) to get it right.
with no accountability to parents or the local authority these views go unchallenged
I disagree - those decisions will be challenged loudly by the public and by the media whenever they are remotely controversial, and the decision makers will need to decide which storms they want to ride and which ones they want to avoid. But then it would be wrong to assume that Local Authorities always made school commissioning decisions that were popular with local people. It just seems that way because most established schools were set up in the days before social media.
Removing parent governors will leave parents with even less of a voice
It was never the role of the parent governor to be a "voice" for parents. They are meant to be representative parents, not parent representatives. I much prefer the idea that parents who become governors are appointed on the basis of their skills not on the basis of their popularity in the playground.
What you may well notice as a parent when your school joins a MAT is a highly paid 'executive head' you'll never get to meet, overpaid and pointless consultants, and an obligatory and expensive silly uniform designed to promote the school that you'll be obliged to pay through the nose for from an 'official supplier'.
That doesn't sound very attractive - but it's certainly not my experience as a parent of children at a MAT school. I guess some MATs are going to be better than others, just as some LAs are/were better than others.