The issue with L3 as Sprint is that a button is so much easier to press and hold than a joystick (as mentioned in the article). Even worse is when games use L3 as Sprint but also configure the analog stick to perform some other action, in which case you can perform actions you don't mean to perform.
To be clear, in games that use L3 for sprinting, you usually don’t need to hold L3, it’s a toggle. I guess there are exceptions of course but THAT would be bad design.
For example, in Fortnite you have to hold L3 to sprint. This causes other issues as well. If you drive a car in the game for example, and use the analog stick to steer, accidentally clicking L3 will cause the car to turbo boost. If you're driving around a corner and have L3 moved all the way in one direction, accidentally clicking L3 is a given which causes an accidental turbo boost.