The Beast Companion reflects the AC and HP changes from being a Beast Master companion, but it does not reflect the proficiency bonus to attacks rolls and damage rolls.

The actions section of the monster stat block is currently just a text block. The site doesn't tag attack and damage modifiers, so it can't change them automatically.

Yeah I get that.. I'm pointing it out here in case it's a thing the Dev's have missed.

I'm sure it is on a very long list of things to redo better when they can get to it.