This is not to blame the supervisor for obtaining few results, but clearly phd students working in large groups or under good guidance can exploit more their potential. Also phd students working in large groups often publish as a co-author just because there is a lot of collaboration within the group. So at the end of the phd students from small groups have had less chances of publishing more.
When applying to post doc positions or fellowship, the applicant must explain what results were obtained during the PhD, the skills that were developed (management, research, etc). Say that during the phd the student did not receive any guidance or support from the supervisor and that the lab only had 1-2 phds and no chance of collaboration within the lab, how can this be explained in a good light and also to show that 1) the student truly acted as an independent and mature researcher without complaining about the lack of supervision 2) to convey the message that the few results achieved during the phd should be evaluated in light of this lack of supervision, and that not being in a large lab did not allow to get those 'extra' papers that phd students in large labs might have chances of publishing.