"...sure you might pick up a foot drag from the dugout, but there is no way a hitter, at the moment of ball launch is looking at a pitchers feet."
-------We are starting to grind water here, as an old friend of mine used to say...
As mentioned in several earlier posts, hitters do not need to specifically focus on the pitcher's post foot during a series of deliveries to notice that "something is different" when a change-up is coming. Good ones will only need to notice that something about the pitcher's motion is different when he throws the change-up.
If a pitcher exerts a different kind of force during his change-up delivery, i.e., any extra force that is capable of making his post foot drag against his forward momentum enough to take off meaningful velocity, I believe that must change his mechanics and timing enough so that an alert hitter can pick up the pattern.
Again, if you are a fairly subtle pitcher and you are not attempting to take too much off with this extra drag force, then probably not every opposing team is going to pick it up...but the ones that do figure you out are certainly not going to tell you about it.
This is not a simple black & white world--there are many shades of grey to this discussion.
The fact is, even if the opposing hitters at your level always knew exactly what you intended to throw on your next pitch you would likely not give up a base hit on every pitch. So, the advantage to the hitter of finding a "tell" is never a 100% guarantee of success--it is a much smaller advantage than that. Nevertheless, when talent levels are relatively equal, success in baseball seems to be carefully built on recognition and pragmatic use of lots and lots of very small advantages.
Just my opinion, and naturally everyone is welcome to their own.