"Work for each other and against wealthy investors" would result in a smaller economy, but the focus is on the positive thing built, instead of just sabotage.
"Smaller" if you're a billionaire. When they say "the economy" just insert "rich people's wealth". It wouldn't be a smaller economy in reality, because what drives a healthy economy is people spending money. Rich people don't spend money, regular people do. Regular people getting paid more and having a larger piece of the pie, counterintuitively means there's more pie.
Only to the extent that withheld labor during a strike affects it. Once the strike(s) are over, an economy that puts more spending money in more pockets will be a bigger one
It turns out that the size of the economy is related to how well-distributed the wealth in it is. If most of the money goes into wealthy pockets and everybody else lives in a sort of poverty-imposed austerity, that depresses a lot of that economy's potential.
What the UAW are after is not a smaller economy, but a more-robust (likely larger) one that includes more people in it.
I think the problems (of high inequality, of unsustainable resource use) are distinct, but related and can probably be gone after by targeting the same things: price gouging and suppressing wages.
If capital can't do those things, labor will have the choice to work less if it doesn't need the money to survive. We've long-since passed the point Keynes predicted (at which, productivity would be high enough to support people at a high standard of living without them working full time) in terms of production, the obstacle to that happening is that capital gets to allocate those surpluses and it keeps most of them
I've spent my career in the tech industry, specifically around open source software.
Corporate powers helped fund the work of individuals for their own purposes, but I can ways we can use them to rebuild local economies instead.
We just need to change how we're using the tools. This can be done by existing skilled workers who are willing to make new choices around who to work for, or by motivated new engineers who have access to the free tools and free training material.