A mortgage is far better than rent.
We can’t magic hundreds of millions out of the air to pay for a stadium upfront, just like most homeowners of working age can’t magic hundreds of thousands out of the air.
FWIW, I think having us as tenants makes little sense. There’s no competition for the stadium. Either we play there or no one does. It has value to Everton FC that couldn’t be matched by any other entity.
So maximum value for their investment comes from the combination of the club and the stadium being one, rather than two companies with two lots of administrative staff and all the other associated costs.