I disagree. A large project can be delivered and paid in stages. Or you can have a state-owned enterprise delivering it. Or any other way that works, because finance system - if for one thing - is 100% a social construct so we have full freedom to shape it as we wish.
The problem with commercial funding is, as I explained before, is that commercial operates on for-profit basis, which means it has to please shareholders in the first place. As result, it prioritises delivering the project at the lowest cost possible. UK is full of bad and very bad examples of how this does deliver projects that are shitty from social perspective — the whole housing market and water utilities serve the primary case studies. UK government is now at the stage of contemplating nationalisation of Thames Water because the investors funnelled all profits out of the company leaving the infrastructure. It was simply not in the interest of all the investment funds to expand sewage network because it was cheaper to dump untreated sewage to the sea.