Just stop. Diminishing returns has a specific meaning and that's not it.
I think what he meant to say is that, compared to the previous amount of damage you did, the percentile change is less. An example:
Say you deal 100 damage. You add a console that lets you deal +10 damage. That means you now deal 110 damage, which is 10% more than you did before you added that console.
If you now add a second console, that will add another +10 to your damage, making it 120 damage. However, compared to 110 damage previously, suddenly you're not adding +10% to your damage, but rather +9.1%.
The idea behind this is that because each console adds a fixed amount, rather than multiplying the previous amount, your damage is increased with a smaller percentage of the amount you had before. I think it stems from World of ********, where players upgrade single pieces of equipment rather than all at once, and dps increases are often measured in % boosts.
It is a form of diminishing returns, but mostly due to the way of looking at it. I totally agree with you that you don't get an additional penalty for adding more consoles.
Don't fall for the fake advertising: Guild Wars 2 is a WoW clone and a poor one too.
I think what he meant to say is that, compared to the previous amount of damage you did, the percentile change is less.
What she meant to do was clarify that the "diminishing returns" that were talked about in the thread are simply a natural function of absolute increases resulting in lesser relative increases when the base value is higher and that, as a result, it's not exactly restricted to one kind of stat over the others.
Why Thissler got so arrogant and aggressive in reaction, I do not know nor do I care to learn.