I'm assuming that the TIE/x1 title from the Raider set can only work on the regular TIE Advanced, not the Prototype, even though the Prototype is technically a TIE Advanced. Would I be correct?

By current rules as written, yes. The TIE Adv. Protoype doesn't include the words 'TIE Advanced' so the /x1 title doesn't work. I doubt this would change via future rules update.

Some will argue Adv. = Advanced though. But since it hasn't officially been released yet, FFG won't FAQ it at this time.

https://community.fantasyflightgames.com/topic/183754-inquisitors-tie-vs-tie-advanced/?p=1712929

Start here. If you still want to discuss it after reading that thread, then we'll talk.