... which is roughly what's being proposed here for iPhone. Since some Samsung devices charge at 45W and require 3A (hence e-marked) cables, one can infer Apple wants to do something similar for iPhone in the future.
Edit: I should add that it is possible for a fully complaint combination of devices to not charge at max(sink power, source power), because not all possible combinations of voltage and current may be supported. For example a 60W charger may support 20V@3A, but if the 60W sink only supports 12V charging, it needs 5A and this combination won't support 60W charging. In practice this should be rare though, it would be terrible product design.
Re: your edit. There is this exact kind of profile incompatibility between the Leviton T5636 and the HomePod mini when two devices are plugged in. The outlet should support 30W for each receptacle, which is more than enough to provide the 18W/20W the HomePod mini requires. But for some PD profile incompatibility reason (9V/3A probably), it does not get enough power.
And it is in fact terrible product design. Leviton is pointing the finger at Apple but in reality, who knows.
IMO it's harder for the source to be flexible with voltage, and especially current limit, so I'd put somewhat more blame on the sink here for not being flexible enough. Generally a sink should expect to be plugged into an 'unknown' source, so should at least make an effort to support multiple voltages.
Designing a multiport power source with a shared power limit is a bit of a tricky problem.