Does your weapon skill affect whether or not your shield styles (like slam) penetrate defenses like it does for your weapon or is it solely based on your shield spec and your dex? For example could a thane spec 50 shield and no weapon, and still be able to penetrate defense trying to slam or brutalize?

In short, your shield specialization, dexterity stat, and +shield skills are the determining factors for landing shield styles. Your other weapon specializations do not affect your penetration chance when using shield styles. So yes – one could spec 50 shield, 0 weapon and land your shield styles just fine!

That said, “weaponskill” doesn’t really determine defense penetration for “normal” weapon specs either but is rather an index value that takes into account things like your spec, stats, +skills, and your class’ inherent ability with that weapon line to give you an idea of how well you might stack up against others.

Additionally, the weaponskill value displayed on your character’s attribute page is only for your “normal” or “main” weapon specialization. This means if a Thane adjusted their Sword, Hammer, or Axe specialization it would update its value but it wouldn’t if they adjusted their Shield spec. You can test this by fully respecializing and then training up your Shield spec. You will see that the displayed weaponskill value does not change.

For Shield spec, there is a hidden “shield weaponskill” value that gets adjusted based on your shield spec, +skills, and your dexterity stat but again, that weaponskill value doesn’t directly determine your defense penetration, anyway.