That is the basis of marxism in a nutshell. It is a scientific framework to observe society and derive conclusions. it is not a set in stone fixed ideology. All real existing socialist projects were and are quite different in practice. And there is a ton of disagreements among leftists about the details. The fundamental common idea is just to create a society that works in the interest of the 99% instead of being controlled by a small capitalist class. How to go about this in detail must change over time since society and the world around us changes all the time. But policies must always be derived from empirical data and the scientific process.

Right now most policies in capitalist countries are created through a very chaotic and mostly unguided process involving competing capitalist interests and the occasional opposing social movements.

Nobody is saying all answers have been discovered, you're confusing political philosophy as a world outlook with a particular formula and set of definite conditions. These aren't the same thing at all, Marxism-Leninism argues against set formula.

Exactly. But knowing what worked for Portugal is just one clue. It's also important to have an understanding of why it worked, identifying other factors that could have contributed, ways the policy can be improved, how effective it would be if implemented in vastly different countries ways to adapt policies to those countries, and even expand the concept beyond drugs.

Imagine a country is going through terrible times and decides to implement some radical austerity measures, sell public companies, defund public services, do all the stuff the IMF loves. Or maybe the opposite, the country nationalizes everything and expels all foreign companies. Let's say a decade or two later the country starts really prospering. It would be unwise to assume this is just universal without proper understanding the mechanics of what happened.