Let me lay things out differently.
I feel that we could have a mixed-member proportional system at the same time as we have a government that takes part in the legislative activity, that is accountable to the legislative power and whose political legitimacy comes from the assembly. We can have a system in which members are, at the same time, chosen by the direct vote of electors in the constituency and also chosen from lists. You could have such a system while still having an executive power responsible to the legislative assembly. There is nothing incompatible in all that.