[Matrixbeast]

Because it's not. Sentai features 6 main characters along with an ongoing story, of course some characters are going to get the short end of the stick.
But a lot of your criticisms all stem from an identical point.

Female characters.

The female Shinken Red plot twist (That lasted for all of 4 episodes?) "Literally the worst."
Your constant issues with Tsuruhime and why the intellectual of the group wasn't a damsel in distress for one of the other 4 men to save more often instead of Seikai or Saizou, the 2 idiots.
You're bringing up that MagiGreen and GaoBlack were bad characters solely because they both valued a woman.
You wanting to remove MegaYellow in place of another man on the team.
It's not about how many focus episodes a character gets, but rather how you personally react to a woman being a prominent figure (Also the notion that women should only get 4 colors, 2 of which are still mostly male (Yellow and Violet) and barring women from being green, red, and black altogether)

So I'll let you know right now. Jetman's primary arc is a love triangle involving Ryu, Gai, and a woman. Gai's rivalry with Ryu doesn't stem from 2 men wanting to push their strength to the limits, but rather, Gai trying to win the heart of the woman he loves.