Low armour for an archer is absolutely fine when they’re perched on a wall somewhere, but the javelin is expected to be in the fight. Get used to hearing the vanguard charge noise, because you’ll be hearing it a lot. It feels like a weapon for another class.
Give javelins to Man at Arms. :D that would be so fun! You’d still have lower armor, but you could dodge defensively and protect yourself more easily to be more proactive in the fight. Wouldn’t be overpowered because it’s still uncomboable and the buckler is a hassle for the jav user. Get close to them and they can’t do much.