I'm convinced they only had Megatron fight Frieza so a Dragon Ball character could win for once, but even so, better matches for Frieza (that he could still beat) would be Thanos or Hordak.
And I don't even know what they thought Starscream and Rainbow Dash had in common.
Dragon Ball characters have won on several occasions. That said, they can throw Goku at Superman as many times as they like, and Superman will always win. Honestly, given how OP characters from that franchise can be, I'm pleasantly surprised when they otherwise lose.