It's a perfectly Valid Example. It's not just 1 second, It's 3.5 seconds, Check all Instances of the Savage Battles logged if you need more infromation in the GCD Timings, Riddle of Fire Increase GCD and raised over-all damage.

This was Mentioned in the OP - I Didn't want to hand hold to give examples for math but fine here's a logical Conclusion for you, If you increase the GCD by 20% for example, then you increase damage output by 20% by Buffing Blood of the Dragon.

This Dynamically changes the opener

Example 1- I've ran some Simulations Mathematically and came to the Conclusion that if you buff Blood of the Dragons effect and add a 20% Flat Damage Increase at the cost of 20% GCD, you are buffing Dragon-fire Dive, Geir, Nastrond, Star-diver not to mention the damage from your DOT.

Example 2 - Gain Results in Dragoon Solving Clipping Issues, Gives Perfect Raid Buff Alignment, Makes up for the loss of Heavy Thrust Indirectly.

Example 3 - Dragoon is oGCD Heavy Already, if you increased damage output by the a flat amount, all oGCDs will be getting indirectly buffed. Nastrod and Jump are the biggest damage Dealers for oGCDs, all the gains end up being near 5% which is around 825 DPS, I Wouldn't call that "Negligible" hell i wouldnt even call it net-neutral

off topic Balance Inquiry : Why isn't Life Surge changed to flat damage increase?