So I will say I never expected I'd get past the 6* challenge with my current lineup (7* maxed Biggs, 6* Wedge G10, 5* Umbaran JC Ghost Phantom with G8 pilots). I did. I don't know if the 5* challenge has gotten significantly harder or not, and I think across the board you need a little more than what the game says you need, but not much (in my limited experience). It takes patience, strategy, and some good RNG. Improve your ships a bit and try again. You'll get there.