For large commercial building yes I believe multiple RIT teams will be required, There is not doubt about that. For our bread and butter fires (the 3 Bedroom/2Bath 1500 sq feet SFR) at team of 4 trained FF should be enough. Our SOG's state that if the structure is over 4000 sq feet than more than one RIT will be established.
By the way we were told in class that Pheonix FD did a study and found that it takes 12 RIT members to rescue 1 downed FF... I found that interesting, but can see where that holds true. We even saw some video that really brought that point home, at the end the FF's were drained and devestated and a brother was lost.