Gone MAD music player had the customizability I wanted in terms of playback. I tried a bunch years ago, and landed on GMMP.
The problem is that when you change cards, the files are no longer in the same place. Even if you use the same file organisation, afaik, android treats it as though it's separate because I've switched cards back and forth, with each card being recognized properly, but not interchangeably despite being an exact copy, having copy/pasted from one to the other.
It you use a file manager like mixplorer, you can see that each card gets a unique identifier. You pull one, slap the next in, and the identifier changes. You slap the first one back, and it gets its original number.
That being said, most music players create and read playlists from media storage. So import/export is easy enough as long as the player has an import option at all.
Poweramp is my player of choice, and it will import system playlists manually. Most of the rest do it by default. Iirc, gonemad and jet do. Been a few years since I checked out the other big ones, but I recall it being a normal thing.
Poweramp is for me still the best alternative with the best file compatibility and tweaks to optimise your listening experience. Haven't found other players with the capabilities of Poweramp. It's also free to try and if you want to unlock it it's a single time purchase license which is very affordable.
Well, yeah, SD cards have unique identifiers, but I thought some apps could ignore it and just see it as "external storage". I'll check the music players, since they have trial periods
SicMu Player is good. Its available on f-droid store.
The thing is SicMu can't create playlists (or at least I don't find that feature), it just play the files located in the same folder
I'm using Phonograph
https://play.google.com/store/apps/details?id=com.kabouzeid.gramophone
It's open-source and shows you all your songs in one huge list instead of artist/album split.
Give Musicolet a try, I recently switched to it after trying a few other players. I think it should be able to do everything that you're after, you can create, import & export playlists. I also sync my playlists from MusicBee on my desktop to my sd card on my phone & found Musicolet to be one of only a few players that would recognise the playlists properly.
A place to ask your questions and seek help related to your Android device and the Android ecosystem.
Whether you're looking for app recommendations, phone buying advice, or want to explore rooting and tutorials, this is the place for you!