I'm not sure if available materials or creature attributes affect worldgen. My observations suggest that, even if they do, the effect is pretty much insignificant. There are four major factors that affect a civ's military success in worldgen:
1) Population size. For elves, it's usually pretty big due to their immortality, but, in some worlds, their civilization gets limited by the size of their home forest biome, so it's hit or miss. You can further increase it by adding NO_EAT and NO_DRINK to the elf raws or by lowering their CHILD age, but I don't recommend that, as in heavily forested worlds this will lead to elfsplosion.
2) BODY_SIZE of the creature. You can raise it up to the human value of 70000 to beef up the elves a little. The side effect is that the dwarves will no longer be able to wear elven clothing/armor.
3) Individual combat skills. These can be adjusted by adding some [NATURAL_SKILL:skill:value] tokens to the elf raws. I don't know if different skills have a different effect on the worldgen battles or not, but if you want to play safe, I'd suggest to add only the weapon-neutral skills, such as DISCIPLINE, MELEE_COMBAT, RANGED_COMBAT, SHIELD, DODGING, SITUATIONAL_AWARENESS. Values of 5 is a good starting point, but you can try and raise them up to 9.
4) Siege minions and their BODY_SIZE values. Any sort of siege minions give a significant boost in enemy battle mortality. For the elves, it's usually pretty good, but is, again, varies from world to world, from civ to civ. You can beef up the elves by adding some guaranteed minions to their entity raws, using the [ANIMAL] token (with all due specifications) followed by the [ANIMAL_ALWAYS_PRESENT] token.