Your "proven facts" are nothing but "fake news". None of those consequences has ever been proven to be the result of speaking more than one language — in fact, with just a little rational thought, you should realize that each of them is impossible to prove.

If they were true, European countries should be way ahead of the USA in creativity and economic output. We have no idea if anything helps to slow down the progress of, let alone prevent, dementia — dementia is merely a symptom with numerous possible (and still largely unknown) causes, and it progresses at very different speeds and with many different manifestations in each affected individual. (Query: How could one ever prove that dementia was prevented?)

The reason that SOME OF the multilingual parts of the US MIGHT have the strongest economies is likely that those parts are the large cities with lots of well-educated (and often wealthy) immigrants who just happen to speak another language besides English.