You're right.
Absolutely pointless, and yet that tall tale of vacuum might scare some newb into opening their door in the rain, or high wind, to lesser the potential of a slide problem.
To put the math into a situation.
Go pickup a 4x8 sheet of plywood and stand into a 3mph wind.
Multiply 4x8 to the size of a slide side.
My little 24.1 slide is 78x78, 42sqft+ vs 32sqft for the plywood sheet.
The 3mph wind would push you down.
10,000 times the pressure of the bellows.
Bigger slide=exponential pressure yet same bellows due to same massive rv leaks.
https://www.google.com/amp/s/www.eng...ad-d_1775.html
Look at that chart and be astounded why a boat can be pushed by a 3mph wind. Lots of psi.