Doesn't seem so much like a battle stance to me, sound more like recovering from the intensity of the fight a little, while Vegeta and Trunks seem more composed since they are reacting to Gohan. I think the fight was more relevant to Piccolo in a way he could barely keep up, which is why reacting to Gohan wasn't the first priority but getting a breath imo, while Vegeta and Trunks were fighting evenly and then more in tune with all the surroundings.In the non-title page, Piccolo is slightly more marked than Trunks and than what we can see of Vegeta's sideface, but nothing major. In the title page, Vegeta's mark looks darker than in the first page, so there's some inconsistency in the shading of damage. The most obvious difference is Piccolo in the title page looks more tired (posture, mouth open). But I wouldn't say it's enough of a difference to say he had a harder time with the Cell Jrs - it could be that he's not more tired, but just happens to be in a battle stance for the cover, whereas Trunks and Vegeta are being shown in their "shocked about Gohan" stances.
But that's just a title page. In the actual page, nothing suggests Piccolo reacts later and his posture is leaning back and not in a (possibly) tired forward posture.Doesn't seem so much like a battle stance to me, sound more like recovering from the intensity of the fight a little, while Vegeta and Trunks seem more composed since they are reacting to Gohan. I think the fight was more relevant to Piccolo in a way he could barely keep up, which is why reacting to Gohan wasn't the first priority but getting a breath imo, while Vegeta and Trunks were fighting evenly and then more in tune with all the surroundings.