well a tbs is different here. In an rts it is almost impossible to play 1vs3.
In turn based games you start on different parts of the world, and you can rarely gang up on 1 single player in the game, because of distances in the early game.(late game you can, but a lot can happen by that time)
So a skilled player can still beat 3 players ganging up on 1 player.
You can do this both in master of magic, civilization series, age of wonders, etc etc.
The reason for this is that early in the game, you are trying to get a foothold in the world, and the truly good players will get a much larger economy and military and techs by the time you meet.
As long as there are not huge penalties for beeing big, the skilled player will have a chance on 3vs1 vs less skilled players.
In civilization series you can cut taxes to 0 once you face a enemy player and just focus hardcore on stealing techs and maintaining a huge army.(this is a cheesy move though, but with enough spies it works a bit too well)
and just how would the 3 players feel if they got beaten when playing 3vs1?