The T'au being surprised by the Imperium's tactics during their first few encounters doesn't make sense.

In the Damocles crusade, the Imperium apparently surprised the T'au navy through broadsides and ramming and the T'au military through bayonet charges and sword fighting. But that doesn't make any sense because the T'au preferred method of fighting is high mobility long distance ranged engagement which should counter the Imperoim's tactics.

In real life, military ships and aircraft can shoot at targets from kilometers away beyond visual engagement. If you attempt moves like boarding and ramming and getting close enough for a broadside it is going to result in your units being blasted down. Same thing in ground battles since modern guns have effective ranges ranging from hundreds to thousands of meters.

Just imagine being the Navy Admiral noticing your Tau enemies have superior firepower during naval engagement and your "brilliant" strategy against it is to rush and ram except the Tau are possibly hundreds of thousands of kilometers away. You're just gonna get filled with holes as you try to close the distance.

Its not to say that close-range combat doesn't happen and even hand to hand combat at times (Note the recent video from Ukraine) its just that relying on bayonet charges and swordfighting isn't reliable against any competent forces with weapons that can kill from hundreds of meters away. Here's an example (0:50) of what would happen btw.

Anyway, its just weird seeing the writer write that the Imperium counters the T'au's strategy by doing something that would be suicide against it. Long range mobile combat counters close range melee combat not the other way around.