When I first started playing Hawken at the start of open beta, A-class mechs ruled. Scouts and Infiltrators were everywhere, and C-class mechs were a joke.
The reason was movement and Armour levels. A-class mechs moved fast, and had to be hit too many times for an average player to kill.
The A-class would dance around the B or C class, take a hit or 2, but get the kill then tank up on the health orb, and rinse and repeat.
It was very common to see 4 or more A-class's (usually Scouts) on 1 team, and they ran in packs like wolves decimating more balanced teams.
Today every mech feels viable, and feels it has a defined role (with the exception of G2's which are a good idea implemented very badly).
I feel that I can kill any mech with any other mech, and that was not the case in open beta.
To blanket increase Armour is a very dangerous game to play, and should be very carefully considered. Even small changes can make a huge difference to gameplay.
The previous dev team got this badly wrong time and again, but did eventually arrive at the most balance state I have seen.