I think that this is a big thing, the original trilogy had three different kinds of force users: Obi-Wan and his disciples (Darth Vader and Luke), who used smallish amounts of "invisible" force powers, but mostly fought with lightsabers; Yoda, who only uses invisible force powers, has a contemplative stance, and doesn't fight; and the Emperor, who mostly has other people fight for him, has no lightsaber, and uses the force as if it were a lightsaber.
The prequel trilogy did away with these visually very distinctive categories.
Anyway, as to the OP, I'd say both, but only on one-to-one combat. Force lightening looks like an attack that, once it hits, cannot be defended against. It is very disabling. Vader manages to ignore it, but he still ends up dead. And the Emperor's faces look like he's gradually increasing its power while he's using it on Luke. I'd say that the first attacks are disabling and painful, and repeating them makes them more powerful, until, when the target cannot defend himself any more, they stop bothering with the "debuffing" and become outright deadly.