Yea, I don't really get where you got button-mashing from because that doesn't work at all in this game. You have a split-second to parry an attack, since you cannot hold it and there's a slight delay before you can parry again.
The whole point in melee is to trick your opponent into parrying early by feinting, dragging your attack, etc. Archers are a thing but you can deflect arrows by parrying at the right time as well, so that gives people without shields a chance.
I'll say right away that this game is more challenging than Warband will ever be, lol. It's basically an updated Chivalry that took some Warband mechanics and created a way more fun game than either. The only thing I'd criticize right now is a lack of maps and competitive game modes.