That's not to say that a boost converter doesn't have value, but it still leaves a gap where there could be confusion.

The confusion or complexity even multiplies if the device has additional USB-C for data transfer. In that case, you either have to mark one port as being the "power in" port, or you have to support power in and data out on all the ports, which gets complicated and expensive.

It would be a great move by the USB IF to think through this sort of thing more carefully. Right now the USB-c connector is so overloaded in terms of power, display modes, thunderbolt, speeds, etc. that it's very hard to predict whether two USB-c devices will connect and at what power or speed and with what capabilities. For power, it would be helpful to require supplies to have a standardized status LED so that e.g. green means that the supply is providing the highest power allowed by the device (not the supply), yellow means there's been a compromise, and red suggests an error condition.

I have converted pretty much everything I have to USB-C, from toothbrushes to old laptops, and am very happy with the results. My solution is to only own high-quality power supplies with good support for PD. Having done this, the question "Why isn't this thing charging?" doesn't really arise.

https://a.aliexpress.com/_Ez4GjPQ

and some powerbanks advertise passthrough charging eg. https://amzn.eu/d/hApICf9

I think there's a soft version of this already available. The term is "pass-through" charging. The power bank that I have [1] will charge itself and the devices at the same time (albeit at reduced rates suitable for overnight charging).

I agree that it would be super useful to have a device that is explicitly designed to provide maybe 5V/5A for a Raspberry Pi 5 without interruption, and perhaps double as a power bank.

[1] https://www.amazon.com/dp/B0DHRYDNXL