Uhh, getting ahead of ourselves a little bit here? Few players play in the Finnish u18 league as triple underagers. I've watched all 4 games he's played this season and he honestly in my opinion is the 4th-best underager on his team(Kiviharju, Vali, Elo all are better), let alone the league. To be frank, it's a bit strange that he's listed as a prospect on eliteprospects while zero Finns are.
Of course, he still is one of the better players on the team but some sense of realism... He's at 1 PPG and would likely need to be at around 2+ PPG for that to be realistic. If we look at players who recently got some u18 time as triple underagers, they would be guys like Kasper Simontaival or Joakim Kemell who were at 2-3 points per game. So far Sisik's season is reminding me of how Robin Keihäs was in C last season. And of course, he got nowhere near B. In fact, he's back in C this season. That's a national team player.
This sort of is the issue with overrating players from all sorts of nonsense leagues like EBJL u18 or whatnot, from marginal hockey countries. You saw he scored at 2 PPG last season as a 4x underager, which sure looks impressive, but in reality he just is a pretty good underager in Finland. And indeed, you don't see these "pretty good underager"-guys getting talked about so much in Finland because they really aren't that special.