I am not sure that is entirely true. I am not saying that you are wrong; all I am saying is that one cannot conclusively make that case. I made this exact point some time in the past, and one moderator of this forum opined that an early, walk-in FP can hasten the issuance of the IL, but it does not necessarily shorten the overall processing time.
I have no reason to be biased here. Admittedly, I am among the minority who have been denied a walk-in FP. Even so, my timeline has been quite brisk, with 72 days between mail in and ID, exactly the same as the case you are commenting on.
In other words, it is really difficult to predict what the USCIS will do. I agree that it does not hurt to try to do an early walk-in. I recommend that one should try it. But, it does not come with any guarantees.