I didn't read the article (and I'm not going to)
10% is either a typo or the person is on drugs.
But the thing that gets me is everyone focuses one the weight ratio. Weight ratio is just one part of a larger picture. (and I know this is going to get lengthy and MANY disagreements
First there's the base what is the upper limit that the horse will operate the best at.
There are three things you look at here (not just the weight ratio).
1. Weight ratio with the horse at a healthy weight (15 hands and 1200 lbs is not a healthy weight). Highest ratio that's best for the horse is 20%.
2. Cannon bone size and density. The cannon bones on most horses are the size needed to carry their weight. Not the added weight of rider, tack, etc.... That's why long distance riders (not you endurance people, but LONG distances that take weeks or months
) should do enough load bearing riding first to build up the cannon bones for the weight to be carried.
3. Loin size. You want good sized loins (short backs are good too when it comes to carrying the load)
That's your base line.
To that you add the physical conditoning of your horse (it's ridden enough and in a manner to put it in good condition for the riding you plan to do). The fit of the saddle (and depending on the kind of riding you do the type of saddle since some saddles, even if they "fit" are not suited for long distances). The ability of the rider (to often over looked).
Now, that's what's best. Not what is normal. We riders love to look at what a horse can do and thing that since they can do it it's fine. We also like to look at what was done in the past and compare it to today.
E.g. Over 100 years ago horses were ridden for days by the Cav on campaigns with weapons, gear, food, ammo, tack and rider.... but the average trooper weight less than 145 lbs (people were smaller on average) and the saddle weight 17 lbs on a horse the averaged just over 1,000 lbs and was far robust than the animals the last 100 years of selective breeding are putting out.
So if we want to make that comparison we'll need to look at what humans and horses are like today.
Can your horse carry more than 20% on cannon bones of a size for it's weight alone with narrower loins and/or a longer back? Absolutely. I'm talking about the best case where the horse has the least negative physical effect Not what a horse is capable of.
Endurance riders routinely ride at a weight ratio that's over 25% and some go over 30%. They ride hard (it is a race after all). Their horses are checked to make sure they meet a minimum acceptable level of condition (which is includes the ability to recover to an acceptable level in a given time)...a bit over simplified, but that's the idea of it. After the race the horse and rider can take a few days break and recover. Has the horse been over extended? Sure, but (in most cases) they've been conditioned for it, they're checked before, during and after to make sure they're not in real danger and they get a nice recovery time afterwards. No much different that some physically demanding and over extending sports that humans do (ever run a marathon?). Some people do the same thing to themselves and manage to live very long, healthy and happy lives (especially longer than a couch potato).
But the endurance riders is the second smallest group of riders out there (long distance riders is the smallest.....how many have you met?), so using them as an example is not really best. (I'm sorry to any of you who are working in the saddle, but while I did that for years LONG ago I have no idea what the numbers are like for people doing that today....30 years later. I do know that your case is much like the long distance riders and the need for a saddle with maximum weight displacement)
Most riders are either wanting to compete in an event or show of some kind or they are just wanting to ride for fun when the can and have the time. They probably don't ride more than a hour or two a day (unless trail riding) and likely might average 10 hours in a week. That's a pretty light work schedule for a horse.
My opinion, for what it's worth (which "ain't" much
). If your horse is a healthy weight (if it's not get it there) and you weigh more than you should, but a healthy weight for you with tack would be within the 25% range (+ or -) for the horse then you can use the weight you're carrying now to your advantage and do load bearing with (ride long and slow and often....easy walking for miles daily is good) to build up the cannon bones (it takes a long time) while you work on slimming down. If you've got a little 900 lbs Arabian that's at the right weight and you're over 6' with a healthy weight of 210 lbs, well, just don't over do it
It's not going to kill (or seriously mame) a healthy, well conditioned horse to carry 25% around for the kind of riding the vast majority of riders do.
If you're a nut case like me and think that anything under 100 miles a week and anything not over a week of riding is just training or conditioning then you really do need to consider and take seriously the base line I started out with (along with conditioning, a light saddle well fitted saddle with a tree that displaces as much weight as possible, etc....)
If you're thinking you want to take up long distance riding......first convince yourself that your not crazy (don't bother trying to convence your family
.....my father went to his grave convinced that I was a nut case from the time I started doing 100 miles on long weekends as a young man back in the 70's). Then train your horse to high line (or stake out...I like staking out), ride your horse for 20-30 miles, camp for the night and ride back home. Do this until you deside that you don't like this kind of riding (even if you have to ride for 3 or more days camping). If you only start enjoying it more then seek professional help. If the Dr's can change your mind and you've already got a horse trained and conditioned just go for it and enjoy (and welcome to the smallest, virtually unknown group of riders
). You'll learn why EVERYTHING to do with the horse is important. Not much fun being 3 or more weeks out and your horse is out with a sore back from the saddle or performance is dropping because the weight is to much or something else goes wrong (and that's not counting the bad weather you'll always end up having to endure
I did say this would be LONG (and sorry for any typos)