Still, cramming everything into a main core had tradeoffs. It's a big core to wake up & run, with significant power draw. If you start running a bunch of stuff, it can be hard to meet realtime constraints, to provide reliable processing where needed.

The blanket statement that more cores is more complicated feels too broad. There's times when io cores are much simpler cinceptually, such as when you have realtime needs such as drones might. Subdivision of responsibility & dedicated cores is a powerful way to de-complect concerns. And it can bring huge energy savings.

Multi-core is also the chip making strategy that actually makes sense. We can cram so many transistors onto a tiny tiny chip, but what do we use the transistors for? We can keep trying to build bigger faster single cores, but there's only so much instruction level parallelism and caching we can actually effectively utilize. Having tiny io cores dedicated to specific tasks can use an incredibly tiny amount of extra die space, while providing incredibly low power dedicated processing for specific subsystems. Seems like a win.

Let's resist making broad statements like "you don't need". What's "needed" might not be what's best. We should have open minds to consider advantages & disadvantages. I for one think tiny io cores can later in amazing possibilities, have seen the rp2040 as a huge leap in capabilities (throwback to the Parallax Propeller with wide SMT like behavior) that's enabled a ton of interesting flexibility & novel low power embedded creations to get off the ground.