Let's review some facts of RTW's reality.
Rome has the second best heavy cavalry in the ancient world.
Rome pays more for seige artillery than anyone else.
The Numidians have immensely weak cavalry.
The Germans can build axe-weilding cheerleaders.
A Roman army can be composed entirely of dogs and pigs.
Egyptian light cavalry can kill any other cavalry unit in the game for a fraction of the cost.
You magically deploy your units before a fight with absolutely no knowledge of how the enemies units are deployed.
Horse archers can't shoot while running. Unless they're running around in a circle, for some reason it's ok then.
No matter how tired your units get they can still run. You can run them in full circles around a desert map for an hour, in heavy armour, in a sandstorm, and they'll still be able to run, albeit slowly, but it's still running.
Your archers and slingers happily shoot their comrades in the back.
Archers seemingly carry individual tinderboxes and can light their arrows in the middle of a blizzard.
Axes ignore all armour but the Dacian Falx doesn't.
Axes ignore all armour but Ballistas and Scorpions don't.
Axes ignore all armour but non-flaming Onager rounds don't.
Repeat the above for maces.
Cavalry, by and large, don't mind charging Elephants.
Egypt rocks at everything.
Scythed chariots are more effective against cavalry than infantry.
Carthage was apparently too confused by the concept of the bow to try and use it.
Pontus has elite pikemen but Macedonia doesn't (Royal pikes use hoplite spears in RTW)
Arcani can hide in the middle of an open, barren desert in broad daylight.
I could list more but I'm too tired. If this doesn't discourage you from beleiving that reality applies to the RTW combat engine I'm sure I know what will.
I'd wager real dollars that after ten games playing Firefox' 'wheel of doom' you'll completely renounce all belief that real world tactics can work in RTW's multiplayer theatre.
On to this:
"Yeah, kinda off-topic, but I think Companions are severely underpowered vs. other cavalry... They can't beat most of the other factions' best cavalry, which is rather annoying."
I don't know about this. They loose to Cataphracts, gothic cav., Cappedocian cav., Legionary cavalry, Desert Cavalry and Preatorian cavalry. But on the flipside they beat Nile Cavalry, Barbarian Noble Cavalry, Scythian Noble Cavalry, Long Sheild Cav (Spain and Numidia's best), Greek Cavalry (Thrace and the Greek cities best), and when using swords they beat Sacred Band Cavalry. I think the problem doesn't lie with Companions being underpowered but rather with a few notable cavalry units (Legionary Cavalry, Gothic Cavalry, Preatorian Cavalry and Desert Cavalry) being overpowered.