Of course there is additional security.

You can't just physically remove the SSD from the machine, place it in another and brute force the encryption.

of course you can desolder and move the chips - all you need is a hot air station and some flux. It's of course harder but nothing even remotely close to breaking the encryption itself, like orders of magnitude easier - any hobbist can do it.

It's another story, a part of the encryption is stored in yet another place on Macs, which it'd be still stored there if the SSD could be moved in/out.