Greeks always fought outnumbered?

[Paralus]

I'm pretty sure what he's saying is that if you count Alexander, then there are further examples (the Battle of the Hydaspes being one) where the Greeks weren't outnumbered.

I do believe that's his point. I'm not certain about the Macedonians not being outnumbered here - though it is more likely they were at least even.

The source tradition for the battle is not at all the best. Arrian reports the attack force as comprising of two phalanx battalions, the hypaspists and their agema, 5,000 cavalry and all of the Agrianians, javelin men and archers saying that this infantry was not much less than 6,000. That number must be closer to 10,000. Once we get to the battle we have a multiplicity of hypaspist battalions and no phalanx battalions. The later have - through either a fault on Arrian's part or via transmission - clearly been missed out.

The total force is some 15,000. This, then, says much about the size of the rajah Porus' army. As does the remarkable statement of Arrian at 5.14.1-2:

[...] because he thought he was superior in cavalry, he took only his horse-soldiers, who were 5,000 in number, and led them forward with speed. He also instructed Tauron, the comnunder of the archers, to lead them on also with speed to back up the cavalry. He had come to the conclusion that if Porus should engage him with all his forces, he would easily be able to overcome him by attacking with his cavalry, or to stand on the defensive until his infantry arrived in the course of the action...

Arrian claims 200 elephants stood across the entire Indian "phalanx" and that these were some 30 metres apart (here Curtius has the more believable figure of 85 from memory).This implies an infantry line of 5.8 odd kilometres without taking into account the cavalry. If these figures be correct then Alexander was, as they say, dreaming. His attack force can hardly have occupied much more than two kilometres at most if we allow 8 deep for the phalanx in close order and 8 deep for the "lights" in a more "open" order plus cavalry.

Another indicator of the size of Porus' force is Arrian's description of its destruction. Here "Alexander himself surrounded the whole line with his cavalry, and gave the signal that the infantry should link their shields together so as to form a very densely closed body, and thus advance in phalanx" (5.17.7).

Many argue that the centre force joined in before the battle commenced or as it did so. that is nowhere stated and a difficult thing to totally miss one thinks. More difficult to imagine is a large force joining an attack underway - especially when it had to cross the river to do so. Arrian only states that Craterus' forces joined in the pursuit of the fleeing Indians after the "slaughter ring" had broken.

I'd suggest any accurate numbers for Porus' forces are lost to antiquity. I'd also suggest that, given Alexander's reported views and the size of his attack force, that the rajah's army was little if any larger than Alexander's forces used in the attack.