Using forward pressure was a means of making Conor constantly adjust his stance and move, it's a way to gas him out quicker. Not only that but Conor's inside game is pretty weak. He's the type that needs distance, space to move in order to throw an ideal punch.
Floyd always changes his style according to his opponent, he adjusts in the ring. That style was the most effective means of fighting Conor.
Someone who had some of the longest reach Floyd has ever fought and knew how to use it reasonably well. On top of being a south paw and having an unorthodox style. Gotta take into account this is a 40 year old Floyd as well. For him, he didnt look good. Technically, defensively, reflex wise. All looked like a shell of himself. So it's silly to expect the same level of performance we've seen from a younger Floyd.
That said, it wasnt just a few rounds either. Rounds 4,5,6 were all competitive and close. 7 was probably the most clear and dominant out of the bunch. 8 was again another close round and 9 was competitive for about half a round then Conor's gas completely gave out and Floyd crushed him.
Even the commentators said through the 8th and 9th round that they're shocked Conor has had such sustained success.
So, essentially what you and others are suggesting is that Floyd took 9 rounds off of the fight. Then decided to go 100%, miraculously around the same time Conor's gas completely gave out.