It's Herms' translation, though. Don't think checking Steve Simmons would be necessary.
Nonetheless, you're correct about that, Ahill. A quick look through the strength checker shows that the usage of steady might actually be the opposite of what I had been claiming. Look at this statement, for example:
Chapter: 325 (DBZ 131), P8.2-5
Context: after Goku and full-power Freeza have fought for a while
Goku: “I quit. [ ] As a backlash from you using your 100% power, you’ve passed your peak, and your ki is steadily dropping…I’m starting to think that there’s no point in fighting any more than this…”
Freeza went from Goku's equal to fodder in 5 minutes, and Goku calls it a steady drop.
Back on the topic... Cutting the Raditz part out since it's kinda irrelevant.
Power IS the most important factor indeed (Albeit not the only one, we both can agree on it), and Vegeta has shown he has plenty of it. So do Goku and Gohan by his own admission, even if the later is in terms of potential. There's no need for Kuririn to have it, specially when all Vegeta notes is that his power is rising, whilst he specifically praised about Goku and Gohan's power:
Chapter: 290 (DBZ 96), P13.2
Context: after Goku says Vegeta can’t kill him, Gohan, and Kuririn
Vegeta: “Well, he’s right. There’s the matter of the dragonballs, and more than anything I need your power to fight Freeza…particularly Kakarot’s…”
Chapter: 295 (DBZ 101), P9.1-5
Vegeta: “We can win! If the 3 of us fight together, we’ll be able to win somehow or another! [ ] It seems that even Freeza hasn’t noticed…These two’s battle power is steadily rising…The squirt in particular hides so much inner strength that he doesn’t even know it himself…”
As for Piccolo and co. stepping back... They sure weren't just "collateral damage" against 50% Freeza.
The true reason they've stepped back is because they're shown to respect Goku's pride and will to fight alone, as shown when nobody other than Trunks is willing to help Goku when he's fighting Cell. They only stepped in against Freeza because it was all or nothing there, with Goku on door's death moments away from fully charging the Genki Dama. So just standing there and watching the fight would certainly turn them into collateral damage.
Sure, Kuririn's power was raising and all and that's good, but per Kuririn's own words such gain has a cap:
The statements and feats presented don't directly contradict such notion; getting stronger and being helpful doesn't mean he can fight Freeza hand to hand now. He's got more power, so he won't waste energy as fast when blasting, kicking or firing Kienzans at Freeza.