b) using the parameter "prune=550" in the configuration you don't even have to download the entire blockchain!
That's incorrect... Even with "prune" mode, you still have to
download the full blockchain, you just don't have to
store the full blockchain.
Also, "prune" mode has some significant disadvantages, such as if you need to "rescan" or "reindex", for instance after importing a private key or address, you'll need to redownload the entire blockchain again.