That was incredibly rude and uncalled for. Please read all of my past threads all hundreds of them to find the answer you so rudely seek.
You said yourself your horse is a hard keeper and has always been thinner..... maybe you're just getting too defensive?
As far as weight, different ppl keep horses differently. Some like a bit leaner horse, some like a fat horse, some like this, some like that. It's preference. A horse can be a leaner weight and still be healthy. I'd rather have one a tad thin rather than over weight.