Communicate your concerns in the most concise and non-confrontational way possible up the management ladder. Summarize the risks, but do not try to impose your conclusion on them. Management must always have the choice of what to do, but it is your job to assess and communicate the situation. Use email, so as to leave a paper trail when things go south.

I hope future historians will be astonished that all of us chose to accept such insanity without doing anything to change it.

Thought experiment: There's nothing stopping this developer from taking the requirements of the project and developing a solution from the ground-up in their language of choice over the course of a couple weeks. The project has been in development for 1.5 months and has 1.5 months to go before the deadline. Their current solution apparently involves relying on a relational database as some kind of programming language or configuration system (100+ tables). There's a good chance that a developer with ambition and talent could singlehandedly deliver a superior solution within a short timeframe.

So what stops the developer from executing? Primarily his own (fully justified) fear of negative consequences. But the only reason his fears are justified are because of structural problems in how companies operate today: managers are expected to drive the direction of the project and are given the authority to do so, and the authority to fire anyone who won't go along with the manager's vision. That makes it impossible for a developer to make sweeping changes and be perceived as doing anything but challenging the manager's authority. But it's not about authority. It's about the customer. It's about making good products. Yet the environment is set up so that the developer concludes that it's entirely justified to be afraid; to sit quietly and do nothing. And it's precisely this collective fear that drives this sort of degeneration within companies.

There has to be something better. I want to try to build something better. Some new way of thinking about how to build a modern software business. Profit sharing, maybe. It might be possible to set up a company such that it could pay its employees a percentage of the profits. The first employee would get 15%. The next employee would get 7.5%, and the next 3.75%, and so on. Then as the company makes profit, that profit is continually paid out proportionally to each employee.

That system has all sorts of flaws, though. One example: an employee should only be getting a percentage of profits while they're at the company. They should be getting their full percentage on day one, and should give up their percentage on the day they leave the company. But I can't think of any mechanism which would actually let a corporation pay out like that. If you tried to pay out profit via dividends, then you'd have to allocate the percentages using stock, and employees don't typically get stock up front on day one -- it takes several years to vest -- and they don't lose it when they leave the company. So profit sharing via dividends wouldn't work.

The idea is to provide an incentive to employees for projects to be useful to customers. There's currently no incentive. Employees are generally expected to play the politics/career game in order to secure a safe future for themselves. I guarantee you that if the employees at OP's company had been given some percentage of future profits, then they would currently be revolting and calling out that manager's behavior and incompetence.