The bonus should be a percentage thing of some form, isn't it? (There's several tiers where the %s factor in, so it may not be obvious; level bonus, level up in general, library, equipment... in LoT1 they were all the same % so scaling lategame was meh, but LoT2 split 'em up) Those with lower base stats tend to have cheaper library levels, though.
100 is sorta low for end-postgame for sure, though. Even the really expensive people. But ones like your main tanks should have extra, while squishies don't need as much in their defenses, as well as characters who overall are barely out for long, etc.
You use spoiler with [spoiler.] and [/spoiler.], but without periods. Being less vague is probably good since it's hard to tell what the semi-final postgame boss is considered to be, although I can guess you mean
. In any case I don't have much experience using tank Komachi, although Rinnosuke with Def/Mnd/HP/Affinity high boosts is pretty beastly and Byakuren/Hina are solid. Once some buffs and debuffs are laid out they shouldn't be having a problem; and as your main tanks, they definitely should have extra library investment compared to the rest of your team.