Yea, I originally thought that too and even worded a response to that effect. But before I posted it I reviewed the card and the book, and noticed the same thing you just pointed out...
On the card: GU-11 Gun Pod Weapon description: "Rapid Fire, RG:24 in Battloid Mode" Notice the comma. meaning the rapid fire is seperate from the range increase. It did not say 'Rapid Fire AND RG:24'
In the Book: Under the weapon description on the Valkyries: "RG 12 (or 24 in Battloid Mode), MD: 6, Rapid Fire" Further making the distinction that Rapid Fire is separate from the Range increase.
On the Card: The GU-11 special function is only listed in the Battloid stats on the front of the card.
On the Card: Under the GU-11 special: "While in Battloid mode Range is doubled and can be used to rapid fire an additional time."
In the Book: Under the Battloid description it read the same as the card: "While in Battloid mode Range is doubled and can be used to rapid fire an additional time."
So the above illustrates, the Rapid Fire is separate from the range increase, indicating that it is a weapon function and not tied to the Battloid mode alone, thus allowing the Guardian Mode to Rapid Fire as it did not say 'Rapid Fire in Battloid mode'. The Fighter mode can't rapid fire due to the Fast Mover rule.
So if the Guardian Mode can Rapid Fire, the Battloid can “rapid fire an additional time." per the GU-11 Special.
But now for the subjective view point... MISSILES! Why would anyone want to go to Battloid mode when you still have those pretty missiles on the wings. Battloid is the weakest form of the three modes IMO. By beefing up the shots and range for the GU-11 in Battloid, it at least gives a use for the Battloid Mode when you run out of the missiles. So I could understand why the Battloid Mode would have a more powerfull weapon.
Just my nickle... with inflation and all.
feel free to poke holes in my viewpoint though.