So one example of a player claiming they were going to gain weight discounts all of the many many times that players have reportedly done that?
What could possibly make it more believable?
The weight of people fluctuates all the time. Have you not also heard that players lose weight over the course of the season?
It is not something that is static. It is constantly in flux.
Muscle weighs more than fat. So when a player adds more muscle they gain weight. I know this from being in the Army which has weight standards that they want soldiers to adhere to based on their height. They want soldiers to be much lighter than they usually are. Very typical for over half the platoon to need to be measured after they are weighed to determine if they are combat ready. When the soldier does extra physical training because of weighing more than what the listed weight, they tend to actually gain weight not lose it, because muscle weighs more than fat. These weigh ins are quarterly and this was one of my responsibilities to keep track of this information and also to work with these soldiers in a plan for them to set goals to achieve the weight the Army says they are supposed to be. The weight changes over the course of 3 months, up or down. It doesn't stay the same.
I completely agree with you that it does not usually matter at all as far as their performance, because weight is not a skill. The player is as good as they are and if they gain weight or lose weight it usually doesn't help or hinder their performance in any noticeable way. That has been my point all along.
One recent instance of a player losing weight and it helping their performance is LeVeon Bell
https://www.behindthesteelcurtain.com/2014-pittsburgh-steelers-training-camp-news-times-schedule-tickets-updates/2014/7/29/5947519/steelers-rb-leveon-bell-dropped-20-pounds-in-the-offseason
I am not sure about the science behind this, but the NFL does seem to believe that the ideal weight for a RB is about 220 lbs. There are many examples of a player being a top performer at lower and higher weights than this ideal, but it is very common for NFL RB who are lighter than this to gain weight and become closer to 220 as a result than they were before or of players who are heavier than this losing weight and becoming closer to 220 lbs. It is something that I have observed about players at this position doing for as long as I have been following football which is over 30 years now. It is pretty much common knowledge whether you choose to believe it or not.