I think you're ignoring the motivation factor. Scotland v England was their major (probably ONLY) target. The way they celebrated a 0-0 showed that. Like a non-League side against a PL side, it was their cup final. I don't think England were "poor" and IF Stones had scored that early chance it would have been a very different game. Scotland, as it proved, as toothless, they created some chances but couldn't convert.
