Pantheon mains, how is duskblade on Pantheon?

It's duskblade.

Every time I go to the forums, people scream that it's OP. Every time I watch a high level streamer who talks about it, they say it's crap.

So I suppose it depends on whether you believe the loud vocal people on forums, or a small minority who are practically playing a different game, and aren't usually theorists. (so both sides have about an equal chance of being wrong)

Duskblade is garbo on everyone except possibly

I've played a lot of Pantheon lately. I think it's pretty great on him as it gives him movement speed and penetration, two things that are valuable to Pantheon's playstyle. He especially needs the movement speed to get within range for his stun. Betewen that, boots and potentially Black Cleaver's passive, you can catch out anyone in the midgame and blow them up. The passive on Duskblade is just icing on the cake. Plus, those two items in conjunction with each other, runes and masteries makes him do close to true damage.