Were not talking about boat speed and VMG or powered megaloops and handle passes. That's not what this thread is about. Its about the start up power available in winds well under 10 knots and the trade off between weight, inertia, shape, drag and duration. In that setting we begin to clearly see the variables laid bare.
I posit that flying an appropriately lightweight/inertialess kite up has more potential power than flying it down for attenuating the power spike and getting you on foil. I generally loop Peaks starting with an upstroke.
Fly a standard kite down and the inertia limits you to a one shot deal, You either have enough power and get up, or you sink as soon as the kite begins to slow. If you fail, its a reset for another attempt. Compare that to Horst working tiny ultra light kites over 20-30 seconds of less absolute power attenuated for longer to produce - high success rate.
Fly a light kite up and you get: added boost from the wind gradient as it climbs. At the apex turn it is in the highest wind, The angle of pull while climbing better suits lifting rider weight over the foil, lastly an upstroke can always be followed directly by a downstroke.
I think that kiters who feel the downstroke is "way more powerful" than the upstroke, are on heavy or high inertia kites.
Just like windsurfing, where a really efficient waterstart technique was key to getting on smaller more performance gear. The intro of ultra light fast kites provides the same opportunity for skilled kiters to get going in relatively low winds on smaller faster kites.