If you're going down this path then perhaps it's worth pointing out that the only long-term improvement of the economy possible is productivity improvements. Everything else is financial engineering which is artificial and cannot last. Productivity is roughly a measure of how much an individual can accomplish for a company.

(Real, meaning subtracting inflation) productivity improvements stopped in 1980, and have been going downhill ever so slightly since. Productivity today is actually a bit lower than, say, 5 years ago. People do less. Now this needs to be measured in real growth to see this effect (although, in the last 6 years or so, even productivity growth without inflation is negative). Attempting an analogy to make it maximally real: essentially, if I have you work for me (as 1 more employee), how many big macs can I sell extra ? The answer, say, was 800, 10 years ago and now it's 700.

Meanwhile, all costs that productivity needs to carry have been steadily increasing, which can be roughly expressed as "per worker, how much needs to be supported ?". For Europe, especially this is very bad (frankly, it is very, very bad for everywhere except the US where it is merely dismal). Essentially, whereas in 1980 every individual working needed to support the life of 1.8 persons, most of them children (who will support others when they grow up), now it's 2.3, most of them elderly (who's main contribution in the future to the economy, as dismal as it sounds, is dying).

This is generally referred to as "secular stagnation". It's a huge problem, because, put simply, the total amount of economic activity we can dedicate to any person is essentially productivity. So you can only get a nicer house if productivity goes up.

In my opinion, it is in fact a much bigger process than the generally agreed upon view above. In 1985 or so the world went from (on very large average) demand-driven to supply-driven. Simply said, in 1975, if a baker produced 5 more pieces of bread, people would buy them, eat them, pay for them, and work a bit harder themselves (maybe making some more windows ... or whatever) to make up for it. In 1995, if a baker produced 5 more pieces of bread, they would rot on this shelves. This is what then causes the productivity stagnation.

Another way to put this is that we are demand-limited. People are producing everything they want (which in economic terms means that they are not willing to work harder for more).

This means that while before 1980 we were arguing "how can we produce more cars ?", "how can we get more people flying/traveling ?", all good questions. Now we're arguing "okay, next year, we'll sell less cars, less people will go on holiday. How do we divide up the profits from that ?". Whatever the outcome, I guarantee not many people will be happy with it.

In other words, the problem is (as stupid as it sounds) that we ... as in humanity as a whole, don't have enough to do. We are embarking on a few grand projects, like urbanizing China, but as a whole they don't seem to make a big difference. We should decide on something ridiculously intensive to do, requiring massive infrastructure build, and go out and do it. Maybe colonize the bottom of the oceans (or the top). Fly to the moon and build a base this time. Capture an asteroid. Or how about automated metros everywhere (or just in many places) ? Whatever. But the alternative is that we're going to have a lot of people sitting on their hands (and being very poor and hopeless and maybe even homeless because of it). That seems like a good thing to avoid.

I must confess that while I wasn't rooting for him, I was hoping that Trump's infrastructure plans would accomplish exactly that, at least for America (and they still might, I suppose), but so far not much has happened.