For argument's sake, I'll accept your premise. (preppers=short term, survivalists=long term)
Then I must ask, which makes more sense to do?
Prepare for highly likely emergency scenarios that have historical precedence, and are known to eventually subside, returning to normalcy?
or...
Prepare for lifelong living in a world completely destroyed, never to recover?
One has merit because it can be accurately predicted based on past events.
The other is entirely rooted in the world of fantasy, as no such life-ending scenario has ever played out on this planet while humans have walked it.
That is not to say it can't. Pay close attention to what I mean.
A rock the size of Texas could hit the planet and "survivalists" might endure longer than "preppers". But there won't be enough to restart humanity, so it would only prolong the inevitable.
Short of that... economic collapse, war, nuclear winter, extreme weather, solar flares, HEMPs, etc... any prepper worth their salt will survive just fine, having already planned to handle a gradient of extremes in their preparedness goals.
Perhaps we should think of this, not as a dichotomy, but as a spectrum.
Sheep->eyes open->emergency fund->3 months of food/water->"prepper"->long-term prepper->survivalist
All "preppers" are on their way to being "survivalists", but self-proclaimed "survivalists" may have skipped some steps, and will find themselves unprepared in their haste to achieve what they consider the pinnacle.
A survivalist is really just a prepper with fewer toys, let's be honest.