Dobby,
The reality of this all is rather simple actually.
One Combat in E:A does reflect a whole game of 40k. This is from Jervis.
Tau used to have great FF values, in fact, it used to be one of JG's design elements for the army.
Tau also used the 'current jet pack rule' for everyone in the army. In other words, EVERY unit used to be able to back away 10cm before the enemy charged.
These two rules together made a deadly combo. Tau could keep the enemy out E:A combat, and when they did get combat, they had to fight on the tau's very good FF terms. These two rules together created something that wasn't intended, Tau charges in E:A.
Tau were so good at FF, that they could back away from the enemy's charges, and could then engage at will with their own FF to crush the enemy.
This was not seen as something aligned with the Greater Good's way of thinking.
The result was to lower the effectiveness by raiding the FF values. That did some good, but in the end, it didn't really help enough as Tau could completely keep the enemy out of combat still in many cases.
In the following revisions, Tau FF was lowered even more, but the REALLY SIGNIFICANT change was the creation of the tau jet pack rule only for tau jet pack equipped units.
Unfortunately, this current Tau jetpack rule doesn't at all reflect what Tau do in 40K with jetpacks... which is exactly what the Eldar really do in E:A. They stole what should be our rule. The hit and run is perfect for tau and is very justified in E:A - but the Eldar took it... ok, don't get me started... I digress.
Ergo our current state of affairs.
Now we no longer get to back away from combat, but we still have really crappy FF.
I think you are correct, FF could now be brought back up a notch in effectiveness (down in actual numbers) as Tau no longer benefit from what was really the problem - everyone having 'get away 10cm before the enemy charges' rule.
According to Fluff, tau should actually excell at FF values (40K) and blow once engaged.
JG must wiegh the balance of doing so.
Right now, I absolutely agree with you. Tau FF are too low and unfluffy for their background.
The greater gooderer would like to see this revised.
Unfortunately, I have no idea when JG will be back in the loop or if he'll post a replacement in his absense. If he would, it would be nice. Perhaps we could make some much needed tweaks in the interum.... but again I digress.