Useless, no. How many times has this been gone over?
A thunder tome is weaker than a wind tome of the same weapon level by one might. I don't hear anyone complaining that most swords are weaker than their lance counterpart by the same one might (same for lances to axes, as well).
Less weight is negligible. Elaice's base Strength allows her to use Elthunder with no AS penalty. She'll average enough Strength to use Rexbolt without AS penalty (14) by level 5 Thunder Sage and Thoron (11) by level 1 Thunder Sage. Similarly, Senerio can use all wind tomes except Blizzard and Rexcalibur with his base Strength and averages enough to use Rexcalibur (12) by level 17 Wind Sage.
The 15 difference in accuracy between thunder and wind (10 for the SS tomes) is partially made up for by Elaice's +7.5 hit from any A support. Furthermore, Rexbolt's additional +3 Skill provides another +6 hit, whereas Rexcalibur's +3 Luck only gives +3 hit (albeit also +3 avoid).
Then, there's always the 5 to 10 critical lead thunder has over both fire and wind, which, though relatively small, is always welcome.
Yes. Not only does her support affinity make up for the (small) difference in hit, she also has a 60% growth for SKL, which is pretty high. I think Thunder tomes suit her just fine.
