Full disclosure, I'm an insider in the industry. I'd like to comment on a few trends I've been seeing.
First, ECUs are now running a general purpose OS rather than a single embedded application. That means compartmentalization of functionality into separate, restartable processes (a program crash is considered a safe failure mode), which is a very good thing. Most synchronization is performed at the low level by the safety-certified OS kernel using very well-known well-understood and well-tested mechanisms, so you don't have to worry about non-experts writing the bad C code so often lambasted in religious screeds. A big advantage is that the software components can be developed, tested, and verified in isolation all using proven-in-use techniquies on a development host before ever finding their way to a target system. The tradeoff is much higher overhead, which with todays processors is effectively noise that disappears into the background.
Second, the CPUs are so fast that manufacturers have developed tickless mode in which most of the silicon gets put to sleep. ECUs these days do much much more nothing faster and in parallel. Things like bigLITTLE make it end up that only 1 32-bit core is actually doing anything almost all the time. So cheaper, less cost, but available when needed. Pretty much all of this is hidden by the OS, so don't worry about your storied ignorant C developer not understanding how to control their software.
Third, somebody not close to the silicon but close to the ledger books looks at all this glorious CPU and memory on an ECU and realizes there are unused resources being paid for and going to waste. They realize they can stick logos on their product marketing material if they start using those spare resources for AI technologies. Yes folks, some of those ECUs are starting to crunch numbers using Fortran libraries driven by Python. From a consumer point of view it's great because the software can now make up for bad hardware dynamically, adaptively, and in real time. From a functional safety engineering point of view, as long as all hazards are mitigated and all failure modes lead to a safe state, it's not a bad thing.
Yes, the silicon in control of your truck is getting bigger, wider, and faster is blooming multiple cores. The software development for it is taking advantage of 70 years of evolution to match. Sit back and enjoy the ride.