Note that at any given moment there's usually a couple dozen daemons running in the background on iOS. And while iPhone will only show one app at once, iPad can do a handful.
iOS optimizes here too, by limiting how much CPU/IO background apps can use. It's frustrating to use Chromecast (for example) on iOS since it's always disconnecting from the receiver.
I'm talking about background daemons from the system, which have different resource limits.
the background daemons are mostly memory-limited, not processor-limited.
Fair. And to be honest, many of them are present on macOS too, without Jetsam around to kill them ;)