There are good players hidden in bronze. I haven't played in that bracket, but I have had a Bronze or two squeeze into Silver while duo queueing, and they did as well as the rest.
I DO think something should change about missing pings. I think the yellow question mark should stay for a lot longer on the minimap where it was pinged. It can simply be translucent so it doesn't interfere with other icons on the map, and/or when pinged again in the exact same spot it disappears. Several times I've missed the ping, or heard it but was simply too preoccupied to check what ping and where.
Since I realize this can happen to anyone, I always double ping MIA, or even triple ping if there is more danger, like a highly mobile person missing (who may be in position to gank another lane in seconds) or I didn't ping as soon as they left.