I’m not sure where you’re getting your info from but apps can’t co-conspire behind the scenes. While a rogue app can get stuck in the background rarely, apps are suspended unless they’re required to be active like Spotify during active playback or calling apps. And if a process is stuck in the background, it will be visible in the battery usage.In theory, yes.
in practice if I have multiple streaming apps like Times Radio and Spotify in the background they can co conspire to run together snd use loads of battery. Hard to reproduce but it has happened.
Personally I close them all occasionally, and nobody can persuade me that having 35 apps in the background uses no resources. RAM surely?
You chose to believe something without any evidence but refuse to accept something that Craig Federighi himself confirmed?