The mortgage repayments are always lower than the rent on the equivalent property.
No. A single counterexample is sufficient to show this is false, but also, it is not true in general.
plus of a pot of money for unexpected eventualities such as structural repairs.
Alice and Ben will need to carry that cost directly.
I have never been able to rent a property for less than twice the mortgage repayments — never … anywhere.
Beware generalizations from one’s own limited experience.
they will likely walk out of any such sale with a profit that Anna and Bob will not only never see,
Depends on how Anna and Bob invested their savings.
Alice and Ben may make whatever changes they like to the property
Note: I never claimed that living in a rented property is entirely equivalent to living in one’s own (mortgaged) property. Of course there are differences — whether these are advantages or disadvantages depends very much on the circumstances.