Are you trying to say that it would be more correct to compare the performance of the teams that played to the performance of the team that didn't play?
As for how long I'd say until there is a notable drop off in talent producing comparing to those years, as being a WJC powerhouse is about the ability to produce elite talent on a consistent basis, as you just can't win the WJC without it (doesn't mean that you're guaranteed to win it though and that's what makes the WJC exciting). And yes, the current state of hockey is that elite hockey talent is consistently produced by 5 countries (with all respect to Czechia there had been a bit of a drop off in that area particularly for 2001-2003 borns, but hopefully they are getting back on the right track), therefore if a team like Slovakia has a strong crop in some year and wins a gold I don't think it will be enough to be considered them suddenly becoming a powerhouse, but like 5 years of consistently contending for gold even without one would mean more in that regard.
