Maintenance for the week of January 12:
• [COMPLETE] ESO Store and Account System for maintenance – January 13, 9:00AM EST (14:00 UTC) - 12:00PM EST (17:00 UTC)
• ESO Store and Account System for maintenance – January 14, 9:00AM EST (14:00 UTC) - 12:00PM EST (17:00 UTC)
It's questionable since it's an official feature on PS4 to allow other PS4 players to play your game, it's up to the game developers to setup disabled areas that prevent this like boss fights.
Shareplay isn't account sharing. The other player is not logging into your account using your details at another location. It's a more nuanced issue certainly. It's money or in game currency changing hands that's actually the problem.