Yes, not all army strengths are implemented the same way. Speed for WDG means something different than for KoE. KoE has everything fast, while WDG has slow mainstay/core and some extremely fast choices outside that. Daemons have Speed as strength very similar to WDG.
FAB? Or read Paths of Magic book fluff and you can relate it to WDG.Occultism is primary WDG path because it is strong and devastating spells path. Like armies that have small spells strength (Ogre for example) have Pyromancy.
Alchemy deals with studying material plane, it is why Daemons do not have it for example. Perfect for someone like a Sorcerer who is close to Daemons to study material plane for them.
Evocations deals with souls, theme that is very strong in WDG due to Warriors making pacts with Daemons, selling their souls to them.
Thaumaturgy is primary a Barbarian path, if we would have Barbarian caster like ADT wanted he would have it. Sorcerers do not have Thauma, because their relation to Dark Gods is different from that of worshipers.
Access to paths do not make the army better or worse, point costs do that. Which paths you have access to gives you character, flavor.
1) Thaumaturgy have literary the biggest devastating spell in the game (wrath of god) and ogres (who has small spell strength) have access to it? Don't you find it to be quite weird?
2) ADT wanted barb caster - why he didn't made it? For book about warriors we have quite a lot of barbarian stuff, barb chief for example was nerfed into the ground anyway.