68f is for sure t-shirt weather. 86f is for sure T-shirt weather.
Who TF bundles up if it's 86 deg.
Super confused, you bundle up at 68f for normal ideal summer temps? Or is 68-86 Gigantic enough you need long sleeves? Or like just low keyed afraid are you of the outdoors at 20c? Spoiler alert... It's nice?
68 is shorts and T-shirt weather in my part of the world. No one carries a jacket around if it's that warm. Maybe it's cold to you if you live between the tropics? I can't speak to that
20-30c is a cool shortcut that F doesn't really have. The original comment is just a decent guideline and "I just don't believe that you can't understand" what a guideline is.
But if you need all this stuff to exist outside in nice weather maybe a quick guideline is not for you...