Good points. For some reason, Firefox does take a second to resume depending on which JavaScript bloated web pages I have open and if those have been suspended for a while, but I assume that this happens with CPU suspend as well. If Firefox was just suspended a few seconds or minutes ago, the resume is not noticeable. I would be willing to deal with suspend-resume during app switching because the times that it takes a while to resume are not frequent, I need Internet based communication stuff to run in the background, and not having the phone die is kind of a plus.
Certain well behaved apps that are frugal with their background threads can be exempt from application suspend, such as the terminal, but not necessary everything that it launches (like Firefox).
I do not know if WiFi 6’s target wake time intervals are long enough for CPU suspend and resume to be viable, but that could be another way of doing it. However, that kind of software development is specialized and expensive.
The main reason why we need application level suspend is to get the battery life benefit while supporting VoIP (SIP) and other IP network communications, like Matrix. Maybe the apps that get suspended will encourage their developers to write mobile device friendly code. Maybe they do not want to optimize for a phone, but laptops are certainly a use case for most GUIs and would also benefit from longer battery life.