LO,
Honestly, I'm not sure I believe the figures for Rafale - but the C delta weight is driven by extremely tough Navair rules for carrier structural design - perhaps they are more conservative than the French. I know that the T-45 weight delta over the Hawk was lost more than 1360 lb.
Yes, I remember those arguments over gun selection, but 27mm is a standardised NATO round and much more effective than the 25mm, especially when you have less rounds to fire. That should have been the driver.
In 03, you are quite right that LM weren't focussing on weight - a major error when designing a jet fighter, in my view. At the time, however, the biggest issue was internal volume, and the Gatling was a volume eating monster. Bottom line was that the US have used Gatlings for many years and didn't want to change. LM went with the flow, very understandably so. The choices surrounding guns are invariably emotive, and in my view this one was no exception.
Best Regards as ever
Engines