So after attending the Office Hourse I came to realise that apparently External Locations are not the ones meant to be used like that and dont support spark. For that you need to still access the locations as per standard access and methods and the storage credential is useless.

HOWEVER, after saying that there is a new feature now in public preview called Volumes that surprise surprise, also have External Volumes. And imagine that, spark works, dbfs utils work, etc. So I guess if your use case involves easily accessing file based content from external storage this seems to be the way to go. On top of that you can use unity catalog for managing access and permissions. Case closed.