BDs, mangas, communauté !

I’m glad to have called it that Jaco will serve as a distraction till Tien comes.
But why is Recoome so surprised at a below 300 power lv. I think even frieza
foot soldiers on namek should be stronger than that. Maybe he is surprised
that trunks can raise his power. Since only mutants could do that, so he thought.

Likely surprised that he could amplify/reduce his power level at all. Sort of like Raditz in the original Manga, he was surprised to see Goku/Piccolo increase their Power Level when using an attack.
Remember, prior to encountering the Earthlings, Power Levels were all static throughout Freeza's Army, or I guess Cooler's army in this version of events. Recoome's reaction makes perfect sense here, he's interested in the ability to amplify his Power Level, but the unit is still low enough that it doesn't actually worry him. Very much a "Huh, that's neat" kind of reaction.

Correction Ginyu was able to control his power level and even Vegeta had some control of his power level. The earthlings just have much better power level control.

Vegeta could only control his power level after the Sayain Saga. Vegeta was a consistent 18,000 prior to his fight on Earth wherein he learned how to raise/lower Ki.
Ginyu is an outlier as though it is stated he can control his Power Level, that information does not remain consistent in his portrayal past that point. He fails to understand this concept when he takes Goku's body and the fact that Goku could raise his Ki to 180,000, surprised him.