Burial Blade and Blades of Mercy

So I did a bit of research into scaling, after starting a Blades of Mercy run in Bloodborne, and now I'm a little confused.

Firstly, the Stats page, when looking at Arcane stat states (emphasis mine):

Despite all trick weapons have an arcane scaling, investing in arcane does nothing to increase these weapons' physical damages. Instead this value project how high its elemental damage would be if it was infused with elemental Blood Gems.

Yet when looking at the Burial Blade or Blades of Mercy (emphasis mine):

Blades of Mercy:

• This weapon has many similarities to the Burial Blade.
  • Both weapons have a direct scaling with arcane towards their damage outputs.

Burial Blade:

• This weapon shares many similarities with the Blade of Mercy
  • Both weapons innately scale with Arcane.

Should I be investing in Arcane, if I want to deal more damage with the Blades of Mercy?

From what I gathered from reading through Bloodborne subreddit in the past, it is known that investing in Arcane in favor of boosting Blades of Mercy won't be worthwhile until you can upgrade the blade to +9.

The tl;dr; version was that you're better off investing in Skill, which scale much better and also boost damage from visceral attacks.