Well, with naked 50Sam/23 mnk, using mumeito(lv1 wep 12 dmg) Get 73-76 damage on normal swings, boost gives me a damage range of 135-138(+62 damage from boost) from initial testing. So either stats make a large difference or its not tied to subjob level. So I should be able to swap to a Combat Caster Scimitar and see +62 damage from boost as well. However with the Combat Caster Scimitar(lv 40 26 dmg) I am seeing ~+99(117-121 unboosted, 217-220 boosted limited testing) . Maybe its partly tied to weapon rank?(Puk-whatever sword, Gae Derg+1, and Hotspur might have same rank)
Working on getting some WS testing in, takes a bit for sekkanoki to cooldown.Will add to this soon as have enough to tell.
Edit - Preliminary results, Sekkanoki'ed Hobaku was doing 194-198 without boost, first one with boost was 222. Need to do a few more though looking like if Boost is modifying WS's it is via a stat modifier adjustment and not adding what it does for normal attacks. So no wonder its not being noticed affecting weapon skills if this is true. Need to do more Sekkanoki'ed Hobaku's to confirm. (again all this is on tunnel worms in south gustaberg)
Edit 2- I have yet to get an unboosted Hobaku to do over 200 damage, and a boosted one to do less than 211(222 highest). Stopped using Sekkanoki to get numbers faster, still getting very narrow damage ranges(its damage isn't tp modified so its to be expected). With the 58 Str I have, and hobaku's 60% Str mod, if understand TP modifiers right would mean Boost would be adding around a 35% to the Str modifier to make up the 22 damage difference on the high end(not too familiar with the formulas)
Edit 3- Went to test to rule out/in weapon rank, and found that boost makes the most difference on normal attacks. CC Scimitar normal attacks got more on 99blu/23mnk, and then pukwhatever basically doubled in damage(~+450) on both Drg and Blu.... So boost is in an odd spot now.