DBZAOTA482 said:
1. Freeza transformed because Vegeta told him to otherwise he would only do it if he felt threatened. Vegeta also outright said Freeza wouldn't change much and he was on verge of becoming a Super Saiyan so in other words, he was being an overconfident idiot.
That slight increase can still be the deciding factor between winning and losing, with Vegeta having no reason to believe Freeza wouldn't immediately transform at any time, especially after the trio had already worn themselves out against his 1st form.
Compare that to against Cell, in which Cell becoming stronger could've been completely prevented by Vegeta's choice and he had no reference whatsoever on how strong Cell's Perfect form would be. The context of both situations are entirely different.
2. The Freeza soldier posed a threat. It was kill or killed in that situation. It's not like with Cell where Gohan was forced to premeditate on bringing the death of someone in order to draw out reserves of power that he can't control.
If you call someone Gohan easily oneshotted in a situation where he could've taken the soldier prisoner, sure...
Gohan also had to premeditate on fighting against the Saiyans and after seeing the losses his passivity incurred was fully prepared to fight them. His actions against Cell were nothing but a character regression.