I would also slightly disagree here... ;-)There are downsides of CF bikes:
That said: CF bikes is the thing for professional cyclists but not really for everyone. In the world of e-bikes, it is not always the more money the better product. More money can buy you a professional but not necessarily practical product.
- Very expensive
- CF is brittle and bike components such as frame can crack and break; which is potentially not only very expensive but also dangerous
- Mechanical work with CF bike requires appropriate tools and care as not to damage CF components.
- It is the best to ride a CF bike on perfect roads...
Your final summary is fine, I CF is not really necessary for all day use and even less with an ebike.
But I have to disagree to ALL your downsides.
- Very Expensive - It depends, I would call it "expensive". If you buy a Expert or S-Works Creo for $10000 or more or a swiss Stromer ebike für $10000, $1000 for the CF Frame (which isn't available for the Stromer, as it would not make much sense on such a heavy bike) would be peanuts.
- CF is more sensible: This is a common prejudice I also had until a few years ago. Here is a very nice video from the producer Simpon (first alloy frame, then CF, then CF single tube, look until the end):
- Mechanical work with CF: You should always have in mind or check the right torque for your screws, also with alloy frames/parts. It's no rocket science and doesn't need a fortune, buy some tools with a torque meter for $20-50, that's it.
- It is the best to ride a CF bike on perfect roads: This point I do not understand. You said yourself that CF frames dampen bad roads, so the opposite is true. Or do you refer to the sensibility of CF frames? As stated above, this is not true (anymore...).
Still no need to spend the extra money for many people and purposes and just rare use of the bike. The CF difference is not that big. But also no reason to be afraid of it.