I pointed it out because it will affect the saddle fit. Also, if I see a horse that's underweight, I will say something - I won't ignore it, sorry. I am glad you have put weight on him.
It is easy for someone who sees a horse everyday to not recognise that the horse has lost or gained weight - some people just do not see that a horse is underweight, so when I see it, especially if there's no mention of "by the way, he has gained weight since this picture" then I will comment on it. I would expect the same if I posted Denny's before picture without any explanation.
I would strongly suggest that if you do post these pictures elsewhere and don't want comments about his weight, please put a disclaimer with the picture. Or post different pictures showing him as he is now, not how he was.
If he's gained muscle and fat, that will change what I would recommend for a saddle or pad, can you please post a more recent picture, and possible one showing him with the saddle on without pads? That will help tremendously.