The Vanguard will get far more tankier than it is now (they haven't implemented the shields yet, and currently it is definitely weaker than it will be).
It is designed as a top-shelf deep space fighter, so taking one down will (I believe after things are balanced) be difficult and pretty rewarding in a weaker single-seat fighter.
That's where "fair" comes in. The Avenger has a significant advantage in maneuverability. That's the card that will have to be played to stay out of Vanguard fire and work to the Avenger's strengths. The Vanguard does (and should) have a big DPS advantage. The Avenger is a smaller target, the Vanguard is a big target, and that's a huge balancing factor.
Also, the Suckerpunch isn't a fully functioning weapon yet, and in BR, it you won't see the advantage of it. BR is most certainly not balanced yet. Ballistic weapons are king, as currently they penetrate both shields and armor. The big ballistic on the Vanguard will do serious harm when it makes contact.
So the TL: DR is, the Avenger vs the Vanguard is a fair fight, and winnable by both parties as long as they play to their ship's strengths.
Even an M50 pilot with a pair of pea-shooters will be able to take down a Vanguard, but it will take a high level of skill from the M50 pilot to avoid fire and keep pressure on the Vanguard until the shields are down.