What would you say Rose is trying to say through the depiction of the Foreman and Juror 6?? I can only think of J6's importance in that he acts like some sort of check for J8, causing him to be certain in his opinion.
Juror 6 can also embody the superficial reasoning that has no place in a jury room

.
"Nice bunch of guys" (shitty reasoning)
"I'm not used to supposing. My boss does the supposing" (or something of that ilk)
"I'm a house painter" (symbol for superficial reasoning, 'surface' reasoning).
He can also be good in some ways that I shaped a whole interpretation around but I've actually forgotten tbh

Foreman's always an interesting one. Maybe Rose criticise the role altogether. Maybe its part of an overarching criticism of the justice system that different rules/regulations have a disproportionate impact on the verdict (role of the lawyers, role of the foreman)... Maybe he's there to highlight that 8th is just a blatantly good leader.