Do you need to be an expert in all 5 schools of magic to gain entry to Winterhold?

How skilled at magic do you need to be to gain entry to Winterhold in the lore? It can't be like it is ingame where any idiot who can cast any shitty level one spell gets to walk in the door. Its been one of the most prestigious magical institutions in Tamriel since the 1st Era.

Edit: They must be pretty powerful though. They got past the undead dragon with Savos. and the other horrors of that dungeon, which should be the most difficult dungeon in Skyrim lore-wise.