Private equity and retirees with everything in a 401k.

This is true - all the global multinationals that essentially make the US stock market earn a good portion of their revenue in foreign currency, so their revenue and profits will increase.

In addition, they are all cheaper when priced in USD, so their stock will go up regardless.

This is just counting short term effect of currency devaluation. Long term there are also effects around trade balance and jobs.

Declining USD makes US exports more competitive.

One could argue that USD is a US export.

Depends very much on the product, it also makes inputs more expensive to buy.

Also, increasing billionaire wealth and burgeoning (but somewhat circular) market capitalizations of companies will seem like a good economy while real income and wealth for the bottom half of Americans keeps falling. The mainstream business media is a gaslight factory completely ignoring the ever-widening K-shaped economic reality that there's a very good economy for the highest income people and a rapidly declining/terrible economy for everyone else.

From an EUR perspective the s&p500 has flatlined over the past year while the msci Europe is up by almost 30% in eur terms.

Needless to say, as an outsider from the inflation bubble, American stocks are not a good investment.

There is a good reason to believe that us stocks will not outperform in inflation adjusted terms over the next 10 years.

If you’re an US investor (dollar-based) who bought stoxx 600 on the day trump took office youre eating very well right now.