Yes that is what I thought since I ride 3-4 times a week for 40-60 mins. I asked my coach he said I shouldn't and blanketing is more for my benefit than my horse.
As for summer he has a fly mask and blanket
I really only blanket my horses if they get cold (shivering or "hunching" for lack of a better word) and during really bad weather. You could split the difference and get him a rain sheet so he doesn't get to hot with his natural coat and the blanket but still stays clean-ish, but I think horses really like their dirt:)
I blanket in fall and winter so my horses don't grow winter coats. Light sheet on cold fall day medium for winter. I do take it off if its 50 degrees or higher and if the sun is out and its really shining.
I let our horses grow a nice winter coat. Then I put a blanket on. But I make sure to get a water proof, breathable one with no insulation. In other words a rain sheet. This keeps them clean and they can still roll and enjoy being horses. An old cowboy friend of mine said he would never leave a halter on a horse unattended but blankets break if they horse gets in trouble so do not worry about the safety issue. Be sure to keep the belly straps short enough and cross the one behind their back legs. Once the temps get to ten above zero or the snow starts pelting for days on end I put a blanket with insulation on. I often feel under the blanket because I do believe a horse would rather be a little cool than too warm. I make sure they never have any sweat. If it is for our convenience that is okay. At least our horses are out in a big field and can run around. This way we don't have soggy horses to brush on rainy days or caked mud to deal with and they do not grow as much winter hair so it is easier to not get them too hot when riding. Already the horses get hot at a walk going up hill because of their nice fuzz. The inconvenient part is the expense of multiple blankets and cleaning and repairing and storing them. But winter riding here is enough of a challenge with the cold and early darkness that blanketing works for me.
I blanket horses Im riding consistently over the winter. Riding isnt natural... so you may need to take some unnatural actions, like blanketing. It can take up to a few hours to cool a fuzzy, sweaty horse off. And you should be using a cooler. If you're lazy or don't have the time blanekting is the way to go, if you ride consistently over the winter.