Riot provided you with a prize being a random free champ in the pool party event. This was meant to get more people involved in the event and as a community we got enough points to get a free champ. Yes, you may receive someone you don't want, but remember there is always a chance to get a mystery prize during or at the end of the season. Also, they don't have to do this; complaining gives them less incentive to actually do something like this again.
P.S. I got Talon for my free champ, but I play ADC's, support, jungle, and top; still happy that's one less champ i need to spend IP/RP on.