It's been a while since I played ME3MP but back then we only went in Plat with my team when we wanted to farm credits/PL a friend who hadn't maximized his manifest yet.
It was ridiculously easy but because we all (or at least 3 of us) knew the maps and our kit perfectly, and we planned our games before going : who is going to do what ? Do we have biotic/tech explosions ? Do we have an Inflitrator ? (Not so much planning was required if we had a sexbot in the group
)
I tried joining Plat pugs and.... well to my surprise, lots of them ran fine. Some were a catastrophe but so are some golds and silvers even so...
When most of my friends stopped caring for credits, we then stick to gold. It was more fun, because you could play as you want in gold.
Oh, I'm sure there are some people who could play with any kit and strange specs (like huh... discoball spec volus engineer with a... javelin ? ^^) in Plat but I don't think that was the majority of the community. I know I could not ^^
I think I can call myself lucky I could find people on ME3 to experience the hardest difficulty. Especially since those people became friends - teamwork has that effect on me ^^