Winner stays on gives my older child twice the turns. Should I change the rule?

My nine-year-old counted their games out loud. "You've had six. I've had three." His twelve-year-old sister replied, "Because I won six."

I'd suggested winner-stays-on for their fighting game because it was the rule my cousins used. I expected close matches. Instead, she knows the combos and he is still finding the block button. He gets a two-minute loss, then watches her play me while he waits.

She says changing the rule now punishes her for being good. I can see why: she's proud of learning the game, and I introduced the arrangement. He wants me to make her play badly, which doesn't sound enjoyable for her either.

We have three people and two controllers for Saturday afternoons. Would rotating after each match be a fair correction, or should I keep some winner-stays-on rounds so her practice still counts? I want the younger one to get actual time with the controller without turning every win into an apology.