Use of Researcher in Pandemic?
Yes, it is perfectly legal for the researcher to share cards on the first turn but it is still somewhat limited, as it is limited to the cards that the player starts with. While it does sound powerful at the start, it should be remembered that it does limit the amount of damage that can be controlled on the first turn if it is spent sharing knowledge. Not to mention that if you are in a 4 player game it would only change someone's hand by 1 or 2 cards, depending on which colors they match in the other players hands, which isn't that large of an advantage when you need 5 cards to do a cure.
2 players: 4 cards to give
3 players: 3 cards to give
4 players: 2 cards to give
Rules

When doing the Share Knowledge action, the Researcher
may give any City card from her hand to another player
in the same city as her, without this card having to match
her city. The transfer must be from her hand to the other
player’s hand, but it can occur on either player’s turn.