Actually you're wrong.
If you cut, make the unf magic longbows and drop them, you get about 635.5k xp per hour. You get no profit from this.
If you cut, bank the logs and make them to unf longbows all at once, you get about 483.1k xp per hour. You also get about 670k for selling the unf bows.
If you cut, bank the logs, make them to unf longbows all at once, gather flax, turn it into bowstrings and make finished magic longbows, you get about 840.1k xp per hour. You also get about 570k for selling the bows and about 9500 crafting xp.
Considering how much different steps there are to creating complete bows and that the finished products always gives more xp, I think the rates are fair.
Also this encourages flax picking and bowstring making/gathering, since they're demanded supplies. It creates a moneymaking method without requirements.
Since non-ironmen can save a lot of time by just buying the materials, it will stay relevant.
Also, I'll remind you that the game isn't balanced around ironmen.
E: Member bonus was included in these xp numbers, but even without it the ratios are the same.