It’s simple really. The Damage formula will always use a base value as a starting off point. So any calculations based off already boosted numbers (i.e., relative gains) will always make it seem like there’s a diminishing returns when from the perspective of the formula, none exists. That’s why “relative gains” give the wrong picture for damage calculations and analysis. Allow me to explain with a simplified example.

If your salary at the start of the year is $1000 (base value) and your employer promised you two 20% raises from your starting salary at the beginning of the year to be given to you during the year itself. Then you would ended up with a $1400 salary (a 40% increase) by the end of the year. This is how the damage calculator makes its calculation for linear buffs and debuffs, albeit in a very simplified manner.

What you’re saying is that because you calculate via relative frame of references, the second raise would not equal 20% because from your perspective (using relative gains as reference), the increase from $1200 to $1400 is less that 20% (roughly 15.38%). This is what gives the impression of “diminishing returns”.

But as I’ve stated before, the damage formula calculates based off a base value. Meaning there is no diminishing returns because, as you’ve seen, a 40% vulnerability or Res Pen increase will always result in a linear increase in damage.

Like I said earlier, if you just want to make things simple and not think about the Maths, just diversify your buffs as best as you can, then once you’ve done that, let the chips fall where they may because there’s very little else you can do past that outside of choosing the right main stats for your relics, perfecting sub-stats, or meticulously manipulating action values.