Um this goes far beyond "not perfect". It essentially breaks every rule in software design, resulting in a fragile, unmaintainable mess.
Projects written by a single person don't need to be developed as academics say. If u were an owner of an exchange and didn't trust to any other coder u would go the same way.
That's why you split up a system in separate parts so you easily can track bugs, or security flaws.
Even if you don't trust other coders.