But I disagree with the higher level idea - that this means that things become simple. It's the other way around - they became so complex that a few person studio cannot write a new, general engine (see how many people programmed Doom or Quake which were state of the art back then!). At Unity there are a few thousands of just programmers working on the engine (yes!). This is not FAANG size, but I don't know if there is a team at FAANG that has a few thousands of engineers working on a single product. You need a team of this size to make a multi-platform, universal engine that is still not good enough to make AAA or open-world games.
Also my personal experience at my last games job (I left games) was the complete opposite of what you suggest as "engines being commodities" (at least this is at odds with you writing that they are working on AAA engines- sounds like they might be "using" engines and not writing in-house ones?). At Sony Santa Monica we had a team of ~30 programmers, out of which ~8 graphics people (just for a single platform and a single game) and I was constantly frustrated with how impossible it was just to catch up on all necessary state of the art techniques with a team of that size.
There are people much smarter than me who spend for example a half of a year on something as obscure as "multiscattering rough diffuse BRDF" - and a larger engine has hundreds of "features" like this.