Shadow was actually a decent spec back then, so I doubt you’d be limited to holy.
That being said, it might seem like there were dead specs but that was the best part of vanilla and that’s what made the game great. Each spec had its’ own role. Druids for example, weren’t the best dps or heals or tanks, but they always had raid spots for brez and innervate. Paladins had a place for their buffs, obviously rogues locks mages and warriors did the top dps cuz all of them but warrs could only dps, mages had food, locks had stones, etc etc.
Every class had a role that made them valuable in their own respect.