That defense is young to WJC and don't have clear leaders + Niku and Tuulola has been only mediocre this season IMO. Few injuries and that defense is one of the worst in this tournament.
Fortunately offence and goalies are very good.
It would be relatively young in your particular setup, but if you oust Niemeläinen and replace him with Sopanen who will bring similar size and add some maturity, it's far from being notably young. Especially since Juolevi would be only player who's still U18 eligible. There's not a lot of depth, that much is true. So fingers crossed there won't any injuries. But if the "best seven" stay healthy, our back end should be far from garbage.
To allay some of the things you question...
-Tuulola in his basic form is good enough to be the #1 d-man in this team. If he's been "good" lately, then it means he's regaining that form.
-Saarijärvi has not had any defensive issues in the OHL, if his plus-minus is any indicator.
-Niku has been mediocre, true, but being mediocre among grown men can still translate to more than decent play among juniors.
-Keskitalo does not look like one of the obvious picks, so maybe we should take a closer look at his liabilities only if he makes it.
-Sopanen may not be the fastest player out there, but like any typical DD, he has sound positioning.
-Haaranen's size has me questioning his usefulness too, but this far, he seems to be doing just fine in Liiga despite it.
I guess the D is lacking that elite leading d-man prospect like Vatanen/Määttä/Ristolainen/Honka we've gotten used to in the past few years, but overall its skill level is still not too far from what's the usual average for us. Besides, I'm counting two or three names who can certainly rise to that occasion.
But if not, even a mediocre junior player playing in Liiga among men is decent enough package to pull his weight in the WJC. If Jalonen just can organize things properly in the back end, there shouldn't be much reason to worry. In which case winning games becomes the seemingly simple matter of outscoring ones opponent. And this is one of those rare years when that does not appear to be a major question mark.
That's true, defense is big weakness for Finland.
If Finland wants to be, serious gold medal contender we need solid stay at home d mans ( Niko Mikkola, Markus Niemeläinen,Miro Karjalainen, Eetu Sopanen) in the team.
Open your goddarn eyes. It's no bigger "weakness" than it is on an average year - the lack of those one or two shiny big names just makes it look so, especially in contrast of the offense. This is such bar corner hockey commenting, almost stereotypically so. The D could be better on paper, but there are no pushovers.
Since one can only bring seven d-men and no backups, that means the selection really needs to consist the best overall d-men we have, rather than simple defensive specialists. So it shouldn't become as a surprise to anybody if Sopanen and Mikkola are the only ones of the type who make it.
Also, there is a very simple formula for not allowing the opposition those dangerous scoring chances - win the puck possession battle. Jalonen happens to be a proponent of that style, and with the offense we have, we can certainly win that race.
Btw, fix those damn quotes. Both of you.