I played in the 1550 elo range before this new league system

I played 2 games and won, went 14-0 one game and 8-3 the next game
but my 3rd game...

Had a diamond jungler who clearly just bought his account

and a Leona support who literally fed bot lane 8 times by just swording in repeatedly(trolling) immediately after getting back to lane as well, then in team fights she would 1v5 sword in with 20% hp before the fights even started. Overall she went 0/10 by the time we were forced to surrender.

Should I expect these types of people lol?

Lol, Some games yes some games no its more the luck of the draw. You need to work how to play around them. Also make use of opposition trolls imo.