Tech companies are qualitatively different in their "raw materials" and "widgets" and "sales". It's hard to see why old rules based on flesh-and-blood products should apply."
...
So, it's different this time?

Well, to be fair, to some extent it is.
It's very hard to come up with examples of historical firms that were gigantic in sales and profits but required trivial amounts of equity capital to delivery their product.

It used to be a pretty safe statement that people overpaying for growth (the statistically usual thing to do) were doing so most often because they overlooked the cost of growth. If a car manufacturer is to grow at 40%/year, they will have to raise capital from debt or equity to pay for the new factories. Both of those are costs that will be borne by current shareholders. But the incremental cost of goods sold for (say) an internet advertising business doubling in size is negligible by comparison. (I know, I co-founded one!) You could say with some confidence that it's really is something the world hasn't really seen before, at least not at scale.

I just think that the amazing economics of these relatively few firms are unlikely to be the biggest explanation of an economy-wide rise in the share of aggregate national corporate revenue ending up in aggregate corporate after-tax profits.

It's not really all that hard to do the math, if one were so inclined. If effective tax rates and real interest rates returned to (say) their 1950-2000 average, aggregate US corporate profits would be down by a lot. A guess based loosely on some articles I've read, maybe a third? Labour share of GDP is down by about about 4.6%, or by 6% comparing the 2010s to 1950-1980. If all that ended up in the hands of companies, that alone would explain the rise in net margins.

It has been a great time to be a capitalist with capital. But such trends can't continue forever...there is only so much pie to divvie up, so the numbers will forever be bound in a range.

Jim