This is a subject that has been argued ad nauseum. Furthermore, we have seen numerous examples of bodybuilders, professional and otherwise, who have built massive amounts of muscle tissue with a wide range of protein intake. Jay Cutler ate about 1 gram per pound, yet was one of the largest bodybuilders ever, while someone like Kai Greene (who is also massive) used to eat as much as 3-4 grams per pound (he stopped that nonsense after switching to Farah). So, there are plenty of examples of guys who have had success eating varying amounts of protein. In general, it seems that most of the larger guys seem to eat somewhere between 1-2 grams per pound in the off-season, when carbs and fats are plentiful.
The latest science might suggest that eating 2 or even more grams of protein per pound of bodyweight is more effective for growth than 1-1.5 gram...and it most certainly would be if one was eating ONLY protein (or subsisting on sub-optimal amounts of carbs and fats), but no bodybuilder trying to maximize muscle growth eats that way. So, when a study indicates that eating massive amounts of protein is more effective than eating more moderate amounts of protein (say 1-1.5 grams per pound), we need to take into consideration that most, if not all of those studies were conducted in the absence of concomitant carb and fat intake.
Many of these studies do not take into consideration the large number of potential variables that could affect the end result. There is a big difference between consuming protein alone compared to protein with a surplus of carbs and fats.
In situations like this, I think it is best to turn to real-world experience for guidance, especially when the subject at hand has been explored by innumerable bodybuilders over several decades. Experience has shown that eating exorbitant quantities of protein during the off-season (over 2 grams per pound) rarely seems to produce superior results in muscle growth compared to eating 1-2 grams per pound (assuming carbohydrate and fat intake is optimal), but it often does lead to digestion issues, additional kidney stress, and other potential problems.
Based on the above, I personally don't believe that eating more than 1.5 grams per pound produces measurably better results when one's overall carb and fat intake is where it needs to be. I just haven't seen the real-world evidence for it. Every now and then I will hear someone tell me that eating 2 grams or more produced better results for them, but I always wonder if there are other factors not accounted for during these situations, as the vast majority seem to grow just as quickly on 1-1.5 grams per pound.
Keep in mind that several other factors can influence one's ideal intake, such as the types of protein consumed, the timing of one's protein intake, how well they digest-absorb their protein, etc.