That is kind of dumb.
The act of stretching a slinky imparts energy which is then released on launch.
Just like a roller coaster at the top of a peak..
The coaster has more energy at the top of the hill than the bottom.
We'd see the same thing as shooting a stretched out elastic band directly at the ground.
No different than throwing a ball at the ground vs letting one drop.
Nothing defy's gravity and there is actually shitloads of tangible theories as to what it even is.
The notion it's a "fundamental force" is pretty much out the window these days.
Research Gravitons
I seen a NASA lab do an experiment on TV dropping a huge feather and a bowling ball..
Both hit the ground precisely at the same time on high def video while watching in super slow mo.
The test was performed in a giant vacuum chamber that you could fit the Space Shuttle into.
It was created in like the 60's i think.. specially created with concrete and aluminum etc.
It's sole purpose was to put space ships into an airless sealed environment to simulate space.
The structure is mind blowing !