The punch without the foorwork is not the VT punch. Footwork required
That is virtually a generic WC/VT principle in my experience, not WSLVT only.
In WSL VT the punch and kick land from the same range. We don't think "now we are in kicking range, we must kick, not we are closer we must punch, now closer still we must initiate the Lap Sau drill". Mostly we are attacking with punches from any and all ranges
You wing chun may be different and that's ok with me
I'll try again. First my point was that it is a biological fact that a leg is longer than an arm. Ergo, in theory, a kick can land before a punch can. Yes many WC forms only use low kicks but there was a reason I noted the issue. "Sweet spots" transcend any particular system.
A "sweet spot" is not tied to a specific punch, nor is it the only spot or required spot to fight in. All fighting systems that are worth a darn have to trained to fight with the flow of the fight. However from a purely style neutral, and analytical, point of view every fighting style has a place to fight that is "optimal" for the style in question. My brother in law is a TKD guy. TKD has punches, even some basic locks and takedowns in close but it's strength is the powerful kicks so it's optimal spot is kicking range. I work with a BJJ guy. His school actually adds a bit more striking than some others (the instructor is also a Muay Thai guy) but still my co-worker's optimal space is grappling and going to the ground.
The same applies to WC/VT. As you say where you can punch is also where you can kick. This range, where we start to have the ability to use all of our tools, is our optimal range.
That is all a "sweet spot" is. Its not a fixed point where one must fight. Fighting is a dynamic encounter where you have to be able to flow in response to every changing circumstances. The "sweet spot" is simply the place of maximum performance.
There is no such sweet spot in WSL VT due to the nature of the punch. Other punches may differ
I understand the nature of the WSLVT punch. Everything you have described with regards to generating maximum power is consistent with my current and former WC. I will acknowledge however that the major focus on the punch is certainly different than my currebt WC because we see the punch as a useful tool and the first you start with but, eventually, we tend to prefer palm strikes for a number of reasons (mostly biological, not strategic, in nature).
Thing is, even if I didn't understand the WSLVT punch at all no functional punch can violate biomechanical laws or the laws of physics. If you get too close, a straight punch, regardless of the source of power, has less strength. Too far away, even if you can connect, the same. Force = mass * acceleration.
The footwork and punch technique determines how you get the mass behind the punch and it's optimal acceleration. Too close and first you don't get maximum acceleration (as that is a factor of distance traveled. Closer still and the effective mass is also reduced due to restricted footwork. This is where I say "thank God for knees and elbows."
To far and you risk overextending your punch. This both reduced the effective mass and the velocity as you are on the deceleration side of the velocity curve.
The "sweet spot" for every punch, especially a straight punch, is that place where your footwork and technique allows for the maximum application of effective mass and the optimal extension of the arm for maximum velocity. Thats physics and biomechanics. It just so happens that because of the preferred kicking method in WC/VT this spot for maximum punch effectiveness is also a place where you can also kick, some styles trap, etc.