"Classic EverQuest" always has and always will mean two entirely different things, neither of which P99 can repeat. Those two things amount to: how
exactly the code on Verant's servers worked, and how everyone
remembers the game working. To say it more succinctly, "classic" can mean classic mechanics, or classic environment.
Again, P99 can never have either one perfectly: the exact code is long gone, and obviously it's impossible to recreate memories of a time when no one knew anything, when we have so much more knowledge now. For the most part, P99 aims for classic mechanics over classic environment. There are exceptions like the mob limit, but for obvious reasons it's simpler to try and replicate old code than old experiences.
But as true as all that might be, can we all stop acting like non-Paladins using Soulfire is completely classic? It's clearly not, by the memory/environment definition of the word. People that remember classic don't just remember Soulfire as "a Paladin weapon", they remember it as
THE Paladin weapon (or at least a stepping stone to it). It was a part of the first epic weapon quest ... before epic weapons were even a thing! (See the
Patch Notes; they introduce epics as "new Fiery Avenger style quests.")
Yes mechanically you could always use it on another class ... but people are lying to themselves if they truly believe that's 100% classic, in every way people actually use that word.