I think the reasoning may be that with Apple you pay extra to know that something will work well out the box without any issues (yeah yeah, I mean the theory). People don't know what FPS is or anything about internals. They connect the device and the video is not smooth. Looks like something is wrong. It is a good approach not to explain to your users that what they see is actually right, but instead find a solution which doesn't make them feel that way.
You don't need to integrate with Apple, there are plenty of solutions. If you do, then there's a reason you use Apple. I think it's mostly that they make choices for users so users don't have to (and it's actually valuable when done right).
Every instance is specific and has its constraints, but there are plenty of high resolution and fps IP cameras sitting in the sun and doing just fine. Most seem to have at least 2-3x power usage. 2W seems really great. Gopros work somehow. So maybe they thermal design could use some improvements.
Using doorbell as a quick check what's happening out there is also a fair use case which shouldn't require somebody standing next to the camera.
I don't know if this lower supported minimum would make much difference in heat though. Maybe Netatmo should be using a chipset that has a lower thermal draw.
Here's what a teardown of their doorbell looks like https://fccid.io/N3A-NDB01/Internal-Photos/Internal-Photo-pd...
And one of the benefits of HomeKit integration is that Apple gives you a certain amount of video storage. The “closed ecosystem” has nothing to do with your ability to use the app. You just can’t integrate with HomeKit. If you are concerned with automation, if their app supports it, you can still use the automation.