Probably the hottest thing there is right now in Poland at such young age, he's got great physical attributes and when given a chance this season under Berg, in a match where he's played the whole match iirc he was voted MOTM and he's looked class.
Problem is though that Legia had those type of players before, midfielders who looked in the league of their own compared to other players and then somehow failed. Dominik Furman who went to Toulouse iirc comes first to my mind can't get a game for shit there, then there was Daniel Łukasik who was touted to be even better than Furman and he's failing at some shittier Polish club than Legia, not to forget Wolski who (albeit CAM and not CDM like those three aforementioned) was tearing this league apart with his dribbles and all that and who failed at Fiorentina and now's been loaned out to Bari just to warm the bench again.
If there's one player in Polish league that's worth looking it and probably will become a big player at some point then it has to be Ondrej Duda. Guy's Slovakian, plays at CAM and there're plenty of big clubs scouting him from Spain, Germany and England. He's sometimes winning matches on his own and will probably be the most expensive player sold in Polish league.
I'd give Bielik 2-3 more years to see how he copes with adolescence, if his body won't feck him up somehow and if he can be a regular at Legia. Believed to be Arse bound by the way.