1v1 Both sides level up in 1 wave.
1v2 Side one levels up in 1 wave, side two levels up in 2 waves.
1v3 Side one levels up in 1 wave, side two levels up in 3 waves.
Seeing as how a standard 1v2 situation means reaching level 6 to two level 4s, for a 1v3 situation, they would all be around level 3 or less.
Now, do you know how fast you reach level 6 in middle lane, do you think you could take down the turret in that time. Even if you did, do you think that would help? This is assuming you're putting three ranged carries (yeah right) in middle to all be underleveled and underfarmed. That is 50 gold a wave per champion per wave, in the BEST situation. Would you like a health pot every wave? Just saying, I could 1v3 just fine without breaking a sweat, easily killing one, been there done that.