Turns are the best metric since they're the only really solidly quantifiable thing to judge by (EXP doesn't even mean anything on its own, same with funds)
But as you're implicitly conceding here, EXP and Funds are entirely quantifiable. It's arbitrary to use them as a standard, but anything other than "beat the game / did not beat the game" is some degree of arbitrary, it's just a question of how many lines we want to draw and where.
The best part is that other factors are pretty much included anyway - if your strategy in one chapter prevented your units from leveling up so much that it slows you down in another, that will end up being reflected in the final turn count
It seems to me that you're saying non-turncount rankings are useless because either they can be converted into turncount, in which case the player should have done so, or they cannot be converted into turncount, in which case they are meaningless. In other words, you're saying that non-turncount rankings are useless because rankings that aren't turncount are useless. I trust you can see why I have an issue with that argument.
If we're equal in skill, then you're not going to maintaining parity, because I'll have used that Speedwings intelligently too, and its bonus will be in play longer, giving me more time to make use of it.
If we're equal in skill and following my assumptions, then we are maintaining parity, because you (like me) would recognize that the immediate benefit from the Speedwings (assumed to be insignificant) is outweighed by the potential benefit of the Speedwings (unknown, possibly significant). In other words, the intelligent approach in this hypothetical is actually to sit on this item.
I fail to see how this is a particularly interesting or enjoyable challenge <_<
I am a born pack rat, and I assure you that I get the warm fuzzies when I see all the stat boosters my supply convoy is lugging around by endgame. I'm not saying I don't believe you, ya dig? I'm just sayin' that you are missing out. >_>
Having to hoard gems in order to maximize FE7 Funds is dumb, though. No disagreement there! I mean, I'm okay with hoarding on general principle as well as to maximize resource fluidity, but gems are literally useless until sold.
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I don't like this duchy. Now, it's an adventurer.