First of all, using these resource valuation to justify a card's necessity for nerf is a bit intangible, mostly due to a long list of assumptions...... Given the situation and meta state of IW, this card at the moment warrants no nerf.I'll admit that there were many assumptions made during calculation, but isn't the meta an equally intangible factor? The anti–Grave meta itself is an assumption that a large number of players use anti–Grave mechanics, and in practice that may not be the case at all.
I'm not saying that I was right, but you aren't completely correct yourself.
I don't know about equally, but the meta is certainly intangible in respect to what the players actually use. For your assumptions to hold ground, you must apply the same criteria to all the cards and compare them. This act as an empirical calculation to whether a card is above or below the standard deviation (whatever alpha you want to use). My argument was focused on the external factors beyond the empirical method of which can construe the results greatly.
I didn't really make any assumptions, I stated what I observed so it can be considered an opinion. However, as you suggested, the volatility in the ever changing meta makes it a bit difficult to justify nerfs based on an empirical method, though it would be a good way to initially balance cards so we don't have to go back and change them later.