Is it true that the A-10 Warthog is not all that effective
Depending on whom you ask it's considered the most lethal and effective combat aircraft in history.
and can barely penetrate tank armor?
You need to be more specific in saying that it's main 30mm GAU-8/A Avenger itself is not very effective in penetrating modern tank armor. It wasn't specifically designed for that role and is a more general purpose air-to-ground weapon. But that only matters if that was it's sole armament, which it isn't.
However, that said the 30mm has proven effective at seriously damaging external optics and sensors on tanks, as well as damaging periscope equipment. This effectively blinds tanks and makes it more difficult for them to respond to threats.
Moreover the A-10 is notable for the wide range of munitions and weapons it's capable of carying externally, making it one of the most flexible attack aircraft. It can carry several precision guided bombs and/or missiles including antitank laser or TV guided missiles like the AGM-65 or GBU-31
Source: Joshua Williams (Quora)
