Preface: I am not a mathematics contributor and have only a basic knowledge of how WNX works, so if this sounds completely ridiculous please feel free to neg and make me look stupid.
Frags should be removed from the WNX formula, leaving damage (dealt and eventually assisted) as the primary contributor to overall WNX score.
The reasons for this idea are not mathematical, as I am aware that frags have a high correlation with winning, but I think a convincing case may be made for this change.
I feel like the foundational question behind the WNX formula is "what factors contribute to a win?", assuming that the goal of the WNX metric is to rate how well a player contributes to the win of a match. Looking at the WN8 formula we can see that the two most prominent factors are damage and frags. But should they both be weighed so heavily? I say no.
Why is damage correlated with wins?
In my experience, most matches are won by elimination, that is, all tanks of one team are destroyed regardless of game type. I'm not sure that this is true across the board, but I suspect it is (even if it is not, there are still valid points to be made). If it is true, then the question must be asked, "what stands between your team and a win over the enemy team?" Some may say kills, but this is not actually true. Though all tanks must be fragged to win by elimination, the only way to get a secure a frag is to move the enemy HP to 0. If all enemy tanks were down to 1 hitpoint, a low tier scout could theoretically load HE and kill them all quite easily. So, in reality, it is clear to see that the HP pool of the enemy team is a far more significant barrier than just the individual frags.
From this perspective the correlation between damage and winning is very logical, seeing that as more HP is eliminated from the enemy team the more likely your team is to get kills and to win.
Why are frags correlated with wins?
Assuming that most matches are won by elimination, frags are made a prerequisite to winning, and will therefore obviously be correlated with wins. It would be quite difficult to get 15 kills and lose.
However, kills are only possible by damaging the enemy, and therefore are a byproduct of damage and not an equal factor. In this sense it seems obvious that both would be highly correlated with winning, but one is a precursor to the other, and in fact supersedes the other in terms of practical significance. Above I said that as your team gets more damage, frags become more likely, and therefore a win becomes more likely, but the base factor in this chain is damage, and other factors depend upon it for significance.
Frags are then, in my view, incidental, and do not by themselves contribute hardly anything to a win. The only situation in which frags contribute highly to a win is when a player eliminates a priority target which threatens the win rather than choosing to farm damage. However, this situation would be impossible to factor in mathematically, and unless some arbitrary limiting factor were to be incorporated to lessen the impact of frags on the formula the only logical conclusion is to remove it completely, leaving damage as the primary factor of the WNX metric.