Framer if you are moving on one travelator that is travelling in one direction than decide to step onto an adjacent one that is travelling in the opposite direction then yes - you will definitely have acceleration issues.
That is the same if you are flying in an airmass that is a constant headwind then you descend into an airmass that is travelling in the opposite direction. That is called wind shear.
I am giving Step Turn the benefit here and perhaps he is describing taking off and climbing from one wind condition and flying into a tailwind condition. Then you will lose performance.
Eg Taking off out of Tehran - 10 Kts head wind, passing through 500 ft AGL you encounter 25 Kts Tail wind - Then your performance descreases.