I doubt that's the case. Thor for example at least has been pretty popular from before, maybe on the level of Zeus, I'm guessing Loki was at least half as popular of a mythological character.
Even separately, I must've read at least 10 fantasy works with a trickster god named Loki.
That’s safe to say. Thursday is literally Thor’s day
From my perspective, Norse mythology was maybe not quite as generally known as the Greek/Roman pantheon (outside of northern Europe anyway). But it was certainly not obscure--at least as far as the Odin, Thor, Loki basics.
I'd be willing to bet that the majority of Americans who can give a vaguely correct answer to Who is Loki? (or Who is Thor?) know that answer because of Marvel at some point in their lives.