Let me remind you that for parkour you need to get to the edge of the block close as possible and then make your jump due to the fact there is no sprinting or momentum. You are wrong if you think parkour would not be ruined. If sprinting was added, players would have to get a running start on there jump which they simply don't need. And for your suggestion of worse case scenario about waiting for your stamina bar to refill is just gonna be super annoying. It's annoying enough that us parkour players have to wait for our health to regenerate after taking fall damage if the health is on, why would parkourist want another annoying issue for us to wait for our stamina to regenerate every time. That's even worse than waiting for health to regenerate since stamina would require almost every jump and health only includes some. Now about about what you were saying about speedrunners. We have speed zones and tenleague boots. Adding a sprint option would only be most annoying to speedrunners for waiting for there stamina bar to refill. Sure maybe your thinking yeah that would be cool because they would have to use there stamina wisely for speedruns as a strategy, but c'mon let's get real, speedrunners aren't gonna want to wait or use stamina wisely. And minecraft players would not be annoyed because we can't sprint. Like you said in the original post, the total miner walking walking is just as fast as the minecraft sprinting so there would be no complaining from them most likely. Now if whay you said is true about a lot of people wanting sprinting, then maybe its possible for Craig to add an option for the world called motion. One motion option would be your sprinting idea and one motion option being the original motion. If that makes any sense to you. This is exactly what happened with momentum and no momentum. People wanted momentum but some people didn't so Craig made it an option if you wanted to enable your momentum or disable your momentum in the player options. Maybe he could do the same for this sprinting idea to enable sprinting motion or enable original motion.
I am all for having it be optional. In general, I prefer making my own mechanics, But this one really cannot be recreated in a professional way with the tools we have.
One thing to keep in mind, You used the example of having to wait until your health regenerates as an analogy for the annoyance of having to wait for your sprint to recharge. In my eyes, A map that is made like that is badly designed. They could easily quicken that process up if they tried. So what does a player normally do if they are getting frustrated by a badly designed game? Generally, They stop playing it and play a well designed game.
A well designed game in this example being a parkour map that heals you when you are forced to lose a large portion of health, Or perhaps gives you a way of healing yourself (Kinda like LB did with creditland.)
One other thing you are assuming is that parkour maps using the sprint mechanic would be exactly the same as the parkour maps are now. That's extremely unlikely for a couple of reasons. 1: There are much more talented people on PC that would be making maps who would be less likely to make badly designed maps. 2: Why would you not design a map around the mechanics you have access to? That's like designing a TM parkour map without utilizing double jump.
To your point of TM walking being faster than MC sprinting, All I have to say about that is that it doesn't feel fast until you slow yourself down. An example of this is the sheer amount of people who suggested sprinting in the past because they felt like they were moving too slowly.
As Alien said, You could do parlour exactly like that with sprinting. You just gotta hold down shift when you are lined up since there is be no momentum.
Lastly, Did I not get an update that added momentum? The only thing I have ever noticed that vaguely resembles momentum is the drift when I am flying, But if I let off the controls, That stops immediately, So it isn't really momentum.