Can someone explain to me why gunblade is rushed first on LB? I typically struggle with it when I try to build it first, so maybe RNG? Also, I started playing LB more, so I'm not the best LB player. I tend to think you lose out on power compared to morello as the first item built. Idk.
In one word, waveclear. The gunblade "discovery" was an attempt to counter the Riot nerfs when the devs decided that Leblanc was scaling too fast. Consequently, when Riot nerfed the W heavily, some bright sparks noticed that the ad/ap combo one got off of Hexblade was a nice way to get Leblanc to a state pretty darned close to where she was before the nerf.
The next stage of the Leblanc wave clear nerf is coming when Riot nerfs the minion damage that Leblanc can do on the Q/W combo - watch for this to come shortly.
I have multiple LeBlanc builds that might depend on the situation:
When you're ahead: 
> 
> optional boots >
> 
> 
When you're breaking even: 
> 
> optional boots > > > or , depending on which damage type the enemy team has more of
When you're behind: > 
> optional boots > > >
