Actually, it really depends on the players+server. That graph, i ASSUME, is for the SST server, seing as it has 50 players on the graph as a varable.
However, on TJW's server, things are different. That server has higher build points, and only 14-16 players max. Also, it tends to have really good ping (because there are not tons of players, and its a good server), and it tends to have expereinced people play in that server.
And the stats for TJW's server dont lie either, it clearly shows the Alien team winning an almost equal amount of times as the human team does.
So, its safe to assume that Tremulous is most balanced when there are a normal amount of people playing, and when both teams use proper tactics for thier side.
Such as, a major problem with "balance" is purly that the players ARE NOT using effective tactics or building placement. The main problem, is that humans tend to let themselves get boxed into thier base at S1, and stay there the entire game. If you can be offensive against the aliens, you WILL win.
Of course, that is hard at S1 because you dont have helmits, and therefore a really good dretch player can kill you in 1-2 hits.
At S2, its EXTREMELY IMPORTANT that the Human team remebers to attack and be agressive AS A WHOLE during S2 (or S1 if you can), otherwise you will just let the Alien team have controll of the map, and box you in your base if they get to S3.
The main thing is, the Alien base is very weak. If you can be agressive, its very possible to make the Alien side crippled even if they get to S3 before you do.
Because, even if the Aleins have Tyrants and Adv. Goons, they are easily destroyed if they have no base to retreat to, and if they have no controll over the map.
This is like basic RTS stratigy here. The problem is that the entire human team often tends to just run+gun and play a RAMBO instead of using RTS-esk stratigy to defeat the enemy, and let me tell you, standard FPS tactics WILL NOT singlehandily win the match. You have to think like an RTS player and an FPS player as well.