This game is actually fairly balanced with F2P grind characters as it is with P2P characters. Look at Lumi, Sid, Phasma, JC, Luke and others. These characters are all top notch and are completely free and can be 7 starred within a month or two. Considering the game has been out almost that long, you can see a lot of older "servers" where F2P players are kicking butt. Not to mention that Bronzium packs can drop 4 star characters as well.
Over time, and with level increases more and more characters will become available for free.