In what way are watches with SIMs (or eSIMs) not just tiny cell phones? Or is you meaning that the modern smartphone is itself a “pile of hacks sitting on top of hacks”?

I just went through this yesterday. My wife and I both have Apple Watches with LTE and I was rolling them over: both phones and my watch ported easily but the second watch wouldn’t show up on the account at all with no explanation. The first support person couldn’t see a problem with the details they were able to see, the second level one could see a fraud hold for non-specific reasons and forwarded us to a fraud team who verified my identity and back to a third person who solved the problem by deleting and recreating the line on our account. Every one of the people I talked to was clearly trying to help but their billing system sounds like it’s someone’s old house primarily consisting of duct tape and stucco.

This is a disappointing contrast to their actual network which is clearly run by people who take running a reliable network seriously with good coverage and latency.