Didn't Goku say that because they would lose the dragonballs?I think it is just Ki. Even after Namek Vegeta still calls Ki “Battle Power” a lot.
However, it seems that Ki and BP don’t translate to literal fighting ability. Goku thought fusing with Mr Satan would be better than fusing with Dende.
He still considered Dende before Satan. Dende isn't a fighter compared to Goku and the Z warriors but he definitely is more skilled and has more ki than Satan and in DB's world having more ki makes you stronger.Goku looks at Dende and says he’s no fighter. There’s no different species, dragon balls or “clearly values him more” here. It’s exactly what it says on the tin. The whole point here is that Dende has more Ki but is not considered a fighter at all.