Packets DO cost more to move one way than the other
In the last 30 years or so that I've been dealing with this we've never reached that magical point where egress and ingress for anyone was balanced (and I would generally consider that impossible anyway). If you are in services, you scale on egress. If you're dealing with end users, you scale on ingress. If the pipe does both, you'll quickly know which one is the most demanding and yes that makes the other direction essentially "free". Given the services they host, these providers are spending on egress so that's what they charge customers for.
As to multi-cloud: mostly in the software. Hardly any of it is truly an infrastructure issue. With some abstraction layers it's easy enough but like it has been for decades: write crappy software and then expect the infrastructure people to magically make it resilient, portable ... Works just fine if you don't take that route and it's not up to the Cloud Provider to make that decision for you, they are not developing your software.
Maybe AWS has a point? Market seems to be misunderstood indeed.