I am wondering what others think... some podcast says "to want a cofounder so that you get a free software engineer is the wrong motivation".
Ideally I would want funds to hire a senior developer to help with prototyping a solution.
An alternative would be to hire a cofounder to do that... as a "free software engineer", which would actually be extremely expensive in terms of equity.
What do others think? Can a full time senior developer start and lead the development of an MVP?
The relationship is gone. It's now a matter of excising him from the business as soon as possible. There is sufficient evidence of him negletting his duties and being unable to fulfil his obligations. To be fair, if he's still around it's probably because you don't have a decent lawyer. Lawyer up.