This very much depends on the lobby. I don't think this is unique to BAR either - it's just that 8v8 is the most popular mode.
Lots of players mean more chances to get a toxic guy who doesn't recognise their own faults and blames others.
I actually just don't really agree about the assertion on player slots. If anything, the better players get the more likely they are to play a front slot, because they have an outside influence on the chances of their team winning.
My OS floated around 10-15 and I virtually always ended up having to go front in every lobby, which is the position I hate the most because I don’t like playing my strategy game like an RPG - that is, micro-ing just a dozen of units and optimising every rocket or bullet hit or whatever, which is kind of what front is like.
Front has zero opportunity or resources available to build any kind of economy, and once the T2 units start coming through from the other side they feel very expendable. As the front player you build the same 1 or 2 units every single game and never really get to strategise.
What also enraged me is that the back players would have the nerve to make the front player “pay” for their T2 constructor units after working so hard to keep everyone alive, despite everyone knowing the front player has zero resources at any given time because it’s all going into units that are being meat grinded.