Oscar is right:
"So, going off the rule book we have the following ordering of outcomes:
Win > 2WD ≥ 3WD ≥ 4WD ≥ 5WD ≥ 6WD ≥ 7WD > loss."
Anything beyond that, though, is contentious and complex.
At a simple level, I evaluate my own performance in the following terms. Without published statistics, I have no idea how many games are drawn at each of those levels. All I know is that, of games played through to a solo, the average performance would be to win just once in every seven games. Anything better than that is satisfactory or better. Anything less than that: "requires improvement". So I divide wins by non-draws. Crude, I know, but relatively uncontentious (please?)
For some time now, I have been contemplating a much more sophisticated system, with measures for the performance of each individual country.
I ask the questions:
if I solo as Italy, what proportion of players (of Italy) have done better than me (none, obviously),
what proportion have done as well as I did? (probably around 10%).
So I award myself 2

for every Italy player who did worse than me & 1 point for every Italy player who did as well as me. And I come up with a percentage of points gained over total available points.
It is a system akin to Match Points scoring at Duplicate Bridge. The comparator is not the opponent at that table. You compare yourself with other players dealt the same hand.
I then ask the same question in relation to two-way draws, then three-way draws, then four-way (etc).
I then ask the same question in relation to the other six countries and compile a matrix of applicable scores ie 7 (countries) x 8 values (solo, 2WD, 3WD, 4WD, 5WD, 6WD, 7WD, loss).
Averaging the percentages in each game gives me a measure of how well I am doing. Some day soon (maybe), I shall research the statistics of historical games to achieve approximations of the values in each cell of the matrix.
That done, the next step will be to take into account the strength of the players who are my opponents in that particular game. There I have in mind a development of the ranking system used in World Rugby.
But more of that when I have done the groundwork.