Regardless of whether you love or hate Electron, its rise in popularity has clearly shown that a number of HN users feel like they don't have complete control over their computer's resources - that their only choice is to either avoid an app entirely or slow down their computers.
A user should be able to pick up an application and easily say something like "you can have up to 2 CPUs and 250mb of RAM. If you want more, come back and ask me." And honestly, if Google couldn't trust that most users would give it unfettered access to 4 gigs of RAM, I bet their engine would magically get a lot more efficient really quickly.
You are often right that you either supply the resources an app needs or you don't. However, there are a growing number of apps I'm seeing that act more like goldfish - they grow to the size of the container they are put in.
I also occasionally run into apps where I'm OK with bad performance, I just don't want them to interfere with other tasks that I have.
I might decide that I'm OK with a version of Slack on my work computer that runs poorly and that occasionally starts caching stuff to disk - as long as the rest of my computer doesn't slow down. Not every app that I'm using needs good performance - some are more important than others. This is especially true for background apps like a backup system, file sync, update, anything where I don't really care if a task takes longer to finish.
It also might be worth exposing some kind of more fine-grained policy; something like "I want this app to have full access to my CPU if it's in the focus, but if I minimize it, I want you to reduce its resources or even suspend it."
And of course there is the (perhaps naive) hope that as CPU and RAM become a resource where users control access in the same way that they control location or camera access, developers might start to include resource-heavy features as progressive enhancements. This has... sort of... worked on the web with resources like location. So it's unlikely, but possible.