I believe it was Fatslob's implied spite when saying it that's making him defensive.
It's more that XII didn't teach Xenoblade anything. I have nothing to be defensive over.
There are some similarities between Final Fantasy XII and Xenoblade Chronicles in its core design. There's nothing wrong about taking inspiration, elements and ideas from previously released games into a new one.
One would have to jump to the conclusion that these loosely based similarities were put into Xenoblade Chronicles because of (or even inspired by) Final Fantasy XII. There is nothing to support that.
While I do agree there is nothing wrong with it. There was just nothing taken or inspired by XII, they are just way too different to come to the conclusion that XII was an inspiration in any way.
If the game in question for inspiration was Phantasy Star Online I could completely see it. The art direction, gameplay, physical appearance (or more exactly the ability to change a characters armor/weapons/ect and therefore their appearance), ect. Xenoblade looks like a single player experience of Phantasy Star Online with an arguably better story (single player stories tend to be better) and no hub world and mission areas (basically Xenoblade is one giant world).
Tell me if you can see any similarities in these.