I've seen videos with the 4x Rets + 1x DK, from WotLK, where one boxer in Arathi Basin can essentially control Farm, Stables and Blacksmith.

Quite a few boxers have mentioned success in Eye of the Storm, which is another 15-man.

I've heard the Battle of Gilneas 10-man strategy of rushing to the middle and killing them there, then rushing to their base and killing them there.
And basically just smashing anything they take, while relying on your team to hold one base for at least some time, and hopefully hold two for part of the game.

WSG... running into a group and killing several opponents, and then camping their graveyard as they spawn... seems to be the only strategy that consistently is reported as successful.
I've never successfully boxed WSG, sure get the occasional win here or there, but I generally don't do this BG.



Bottom line seems to be...

10-man BG's can be successful with a very specific strategy, but your team needs to be much more geared than the average opposing player.
And the strategy won't always work.

15-man BG's we see some success in.
Again, once our team is fairly geared... but 3 or 4 players who chain CC us or a single rogue can make life miserable for an entire 5-man team.

40-man mass BG's...
It is not a penalty to have 10 players in one place, most of the time.
Defending or taking a Captain or General, this is great.
As is having that many or more, at any mass pointless (for objectives) battle like the Field of Strife... but holding a choke or breaking a choke can get a win too.
I have no problem killing groups of 1-10 players in most AV's, over and over... but have had groups of three that prevent my five from retaking a bunker... and once the bunker burns and we exit, they drop in 4 seconds for all three of them, having a quarter of my resilience.
The larger BG's favor boxers more so then the smaller.