It's taking character agency away from Scootaloo for her to only be saying that because Lightning Dust _manipulated_ her into thinking that. It also doesn't convince me you aren't grasping for straws, when there's also not a single quote that _implies_ anything of the sort.
It _is_ "Normal Scootaloo," just momentarily pissed off at Rainbow Dash, and you have no proof "Normal Scootaloo" _wouldn't_ accept that she'll never fly. You're willfully ignoring
each and every implication in favor of your own views that have nothing to support them.
In short: assertions presented without evidence can be dismissed without evidence, and you don't have any evidence whatsoever to support your claims.
Why can she stand on clouds without a cloudwalking spell applied to her, then, if she's just an Earth Pony with vestigal wings?
I'd tend to think something along the lines of her pegasus magic is two-dimensional, when it should be three-dimensional, so while she can propel herself very quickly horizontallly (to the point of going faster than a speeding train while towing the other two Crusaders), she can't fly for that reason.