"Economics is not based on solid science"

Pretty broad statement. Some micro-economic theories, like the game theoretic models in auction theory, contract theory, mechanism design and behavioral economics are probably the most successful, accurate and impactful theories in all of social sciences, including psychology.

You may not realize how much your buying behavior, your salary, your interactions online and your use of technology are dependent on these models. But comparing their success and use to fields like sociology, management and even psychology, their track record is frankly amazing.

We already know that Macroeconomics amounts to modeling systems that do not aggregate meaningfully from these successful micro-models.

Saying economics is not a science based on this, is like saying physics is not a science because we still can not find a unified theory. Which is a pretty good analogy for a Macroeconomic model that forecasts GDP (aka, everything).

There are also no ways to run experiments in cosmology.

The difference is that you don't try to act on the cosmology models to change the way galaxies behave. Most of practical economics tries to derive policies or make choices out of its models.

That's irrelevant as far as the designation of "science" is concerned. This is a question of knowledge and certainty, not practical application. The point is that results in cosmology (and other fields) are very well confirmed despite the fact that they don't come out of strict experimentation. In that same vein, when someone denies that economics is a science I'd argue they're really talking about whether its results are robust, not whether economics uses a certain methodology or is put to certain ends.

No, you don't. But having the complex macroeconomics models far beats relying on layman's guesswork.

You've never looked at a macroeconomics model, have you?

Economics is complicated because it is modeling the behavior of human beings.

Math is easy, computer science is easy, modeling the collective behavior of humans is hard.

On the contrary, cosmology is based on physics (gravitation, Maxwell equations & so on) and a good bit of chemistry. 99% of the knowledge used in cosmology is based on science science developed and tested "in vitro" on Earth.

But you still can't run experiments on cosmology. SO if your definition of "science" is "based on experimental data", cosmology isn't a science.