I mean going around telling something won't age well is a fairly risk-free strategy unless you can point out any actual arguments to support it. If he was on par with at least the best players in the SHL he would have made the Swedish WC team (or numerous EHT teams before that). And even then very few of the best SHL players have NHL potential.
How is it a risk free strategy? If he doesn't make it, I am wrong you are right.
Now, as for the arguments. You mentioned the main one already, 2 games is a small sample size. When oeple were saying that Mozyakin will not be able to play in NHL it was backed up by large sample size of his underwhelming international play. Here, we are talking about 2 games and you have the reaction that he has "snowball in hell chance to make an impact in NHL" which is a hot take.
Second, him not being selected by the wise and learned hockey scholar Garpenlov who coached Team Sweden to its worst result since the 30s means not much at all. First, his team selection ablities are questionable to say it politely, second, Dahlen had long playoffs and wasn't able to be on the team in the camp and Garpenlov decided that he was not in the pool of players to invite after the EHT.
Now, on the comparsion with SHL players, and making the EHT. He made the EHT. And aside from 6 players(Friberg, Pettersson, Zaar plus the Seklleftea line of Berggren-Wingerli-Froden) nobody played more than 3 games this year. Playing in Allsvenskan he already was put into much harder position, for example, Carl Soderberg who I think we can agree made some impact in NHL was selected only for 4 games of EHT for 4 seasons from 2008 to 2011 and all of them happened in the same year, and of course he did never make WC during this period of time. And this was despite the fact that he has "proven" to be SHL quality in 2007 when he had PPG there. When a player is playing in Allsvenskan, unless he is a Kenny Jonsson level celebrity he already is fighting an uphill battle.
Dahlen didn't play in SHL we can't compare to the "best SHL players" but he had a completely dominating season in Allsvenskan, which is a fairly good league and he dragged Timra to SHL this year, it's not just individual stats, it's also team winning the main prize of the league.