Not quite analogous. We know many problems with Capitalism, and we know many aspects of leftist organization absolutely work. We know what parts historically did not, and we also know that these issues are far from necessary for building a leftist structure.

You're arguing that there's no point in improving the plane and fixing what is broken when we still have cars and horses.

For your point that it could be that the screws can never be tightened, or a solution without screws cannot be found, is not an argument against tightening the screws or coming up with an alternative method, despite pretending that's a valid reason alone. In fact, in Engineering, it can be known what forces will be applied to screws in flight and as such it can be predicted what is required.

Essentially, you can use previous knowns to solve for unknowns, rather than assuming everything is simply a blind guess.