^ What should actually be done in these cases is use an Acrobatics (Str) check. Or I suppose an Athletics (Dex) check. Either one could reasonably describe parkour. As Niara said, muscles are certainly involved in jumping, so str or athletics should be involved somehow.
My character is carrying multiple suits of armor, leather and ring, along with 4 short swords, 2 great swords, 29 potatoes, and a couple of backpacks, in addition to a nice, framed landscape painting and a half dozen goblin bows. Oh yeah, I've also got some daggers and crude maces stuffed in a pocket somewhere. In addition to all that, I have a personal shield that I use, and when I'm not using it, it disappears into my back along with all the other stuff I'm carrying. Nothing about this makes sense, but whatever, let's go with it for now.
Meanwhile, Astarion is beside me. He's carrying next to nothing, just a potion and a couple of scrolls.
I can still jump much farther than Astarion. Because he's so weak, and I'm apparently so strong, and the weight I'm carrying doesn't seem to matter too much.
What I'm getting at is that none of this is real world physics, and none of it makes sense under a magnifying glass. I don't want to say it's necessarily disingenuous to talk about how a Dex based Acrobatics skill wouldn't work, but it's maybe a touch misguided, imo.
Sure, in the real world Acrobats are pretty good jumpers. Sure, in the real world, Acrobats have trained their muscles. Sure, in the real world, you could measure the muscle strength of an Acrobat.
But in this world, Acrobatics is a Dex based skill. These skills are only an approximation of things. It's a reasonable call to say that someone with a high Acrobatics skill but a low strength isn't a power lifter, but does have some measure of strength in the right areas to accomplish the impressive feats that acrobats are known for.
It's also nice to have a lithe, Dex based fighter being able to jump around and leap from balcony to balcony while fighting the extravagant battle. Because it's cool and it feels fun, and it's at least as realistic as anything else going on.
Now, if the argument is that it unbalances the game and lessens the value of Str by too far a margin, that's an argument to be had. I don't agree, but I understand why someone might put that forward as a concern. But saying jumping requires muscles? Shrug.
Just my opinion.
