Paralysis is effectively silence, since they cannot cast, or do or say anything.
1. it's no longer in the same skill tree, so a mage/hybrid character relying on illusion who doesn't want to level alteration
can't cast paralysis2. No, it's not the same. Paralysis is a short spell that is meant to basically stop an enemy in their tracks for a very limited period of time. Silence is meant to be used on magic casters and it lasts longer than paralysis, giving it an advantage over paralysis for killing mages.
3. A does not equal B.