I once work for a giant fortune 500 corporation. Our department had a good 300 developers, and had been writing code for years. They had built the whose system using the classic, box-box-cylinder architecture. There were hundreds of little top tier 'services', but in practice, they all shared the same database, had to be deployed pretty much at the same time, and version upgrades had to go in lockstep. Every so often, database changes were necessary, and the world would grind to a halt for months to make the system still work after the migration: It was awful.
On top of this, having everyone using one stack really meant that a council of elders got to make tech decisions, and everyone else just did what they were told. This built a giant hierarchy. People near the top would never leave, because nowhere else would give them that much power. Talented developers would take years to gain influence, so they often just left. What remained was developers with no ambitions other than getting a paycheck... it was horrible.
The alternative was to let people maintain their own stacks, as long as they provided interfaces that other people could call. By limiting how much code could talk to a database, you didn't need negotiations to change something: Teams made any change they wanted as long as they remained backwards compatible, and then had to lobby users to upgrade to newest API versions if they wanted to remove the backwards compatibility mess. It was awesome in comparison.
A gigantic place won't have those problems, because they can invest money on making whatever tech decisions they made tenable: PHP is slow? Let's build a new runtime and compiler, says Facebook! If you are tiny, you don't need any of this BS, because if your team of 8 engineers can't agree, your company will fail regardless. But when you have 200 engineers, it's giving people more control over a piece of the pie or bleeding talent.
The one thing you still need to do is make sure teams have the right size, and people have enough accountability, that the product still works. You also need silly amounts of data marshaling and error checking compared to the monolith. But the terror of a company that can't hire engineers because the only way to have any control over your daily life is to have been there for 5 years is just hard to compare. When people say they don't want to work big corporate gigs, what they really mean is that monoliths become soul sucking.
So yes, I give thumbs up to fiefdoms, just like I'd rather have inefficiency in a republic vs a theoretically efficient dictatorship.