I’m no draft guru, but from watching the WJCs, none of the lottery type players look like they could step in next year and make an immediate impact like a Matthews or Laine. I think this years pick is going to follow the normal path and take 4-6 years before they start playing top minutes at the NHL level.
The WJC heavily favors D+1 and D+2 players.
There are three major international tournaments draft eligible players compete in:
Hlinka Gretzky - Conducted at the beginning of the year, and it only allows players who are 18 and under as of December 31, [year of competition]. So this year, the 2019 Hlinka Gretzky only allowed players born after Dec 31, 2001. Lafreniere did not compete this year, as he was born in October. Rossi did not compete because Austria is not a participant.
WJC U20 - Conducted the day after Christmas > shortly after Near Year. This has all players who are under 20 as of December 31, [year of competition]. Thomas was 20 years old when he scored the gold medal-winning goal. If he was born three days earlier, he wouldn't have been eligible. Not too many first year draft eligibles make it here due to the more physically developed and skilled players. Rossi did not compete in this tournament, as Austria was relegated to one division below (though Austria DID compete earlier in the year, and per Rossi, he was told by his agent not to participate, which is weird, but I'm digressing).
WJC U18 - Conducted near the end of the hockey season (this year, it begins on Thursday, April 16). I *believe* the restrictions are the same as Hlinka Gretzky, so even though it's in April, you'll still see players who already turned 18, even though it's called the Under-18 WJC. Either way, you'll see a larger chunk of draft eligibles (as well as some future drafts) participate.
Keep in mind there are other tournaments, but are more locally focused. For example, there's the CHL Top Prospects game, which features only draft eligibles, and they are only drawn from the CHL (which includes the OHL, WHL, and QMJHL).
These tournaments also have some context which need to be added:
Canada typically does better in the Hlinka Gretzky Cup, as they draw from a very large pool of draft eligible players. The United States typically does NOT send players from the US National Team Development Program. They'll send eligible Americans from other leagues, so Alex Turcotte, Cole Caufield, Jack Hughes, etc don't attend this early season tournament.
The United States typically does better in the U18. Because of the timing in the tournament, Canada sometimes has a lot of their players still playing in the playoffs. Conversely, as the US NTDP has spent all season playing together against college and USHL teams, Team USA will send that team to the U18 (so players like Arthur Kaliyev, Nick Robertson, etc do NOT attend this tournament). Players like Jack Hughes, Alex Turcotte, Cole Caufield participated in this one.
There are a lot of reasons, aside from small sample size, that these tournaments can't be independently used to scout and determine readiness. It certainly provides important information, but to assume no player will step in and make an impact right away based off one tournament is faulty.