Correct me if I'm wrong, but I once read that quitting an app to "save power" actually could use MORE power than just leaving it alone, atleast on iPhones. Is this true? Also, there isn't a meaningful difference in RAM saved, right?
Correct. If you launch that app often, you are forcing the app to go through its startup process every time you open it, as opposed to just reawakening the app from it's cached saved state. Probably not a big battery difference for most apps, but force quitting is certainly not a way to "save" battery for 99% of apps.
It also could lead to unexpected consequences, such as lost data, since the author of the app has no way to predict when an app is shut down with zero warning. If you have legit reasons to be running processes in the background, such as Bluetooth, this can totally break functionality and lead to massive support headaches.
There is no real difference in RAM. Unless that app is doing some necessary background processing, which is mostly granted for seconds only very occasionally, and only if RAM is available. When an app goes into the background, it is effectively shut down as far as the system is concerned. And if the system is running low on resources, it will kill any process with impunity in order to keep the system up and running.
There are some apps that will abuse loopholes to grant themselves longer background privileges. In my experience, Apple eventually fixes these loopholes and forces the app maker to change their strategy. The days of apps turning on your microphone or playing silent background tracks just to stay alive while backgrounded are mostly gone now.
As I mentioned before, any apps still getting away with this sort of trickery are not worth using.
The bottom line is your iPhone knows a lot better than you do how to handle memory and battery management. Unless you truly have a malfunctioning app, or you have a very good reason to suspect a particular app is eating your battery needlessly, the force quit mechanism is best left alone.
Certainly, habitually quitting all your apps several times a day is at best a waste of time.