You want to train wrestlers with shields. There are five ways to protect against bowgobs: walls, fortifications, dodging, shields, and armor. That's the preferred order. You're looking at it backwards, armor is the last line of defense. Much better to stop the bolt with a wall or to dodge or block it than to try to absorb it, even masterwork steel can be punctured by an elite bowgob's iron arrow if the recruit wearing it takes a bolt to the face.
A few other things.
1: Don't worry so much about weapon grade if you can train soldiers. I've had legendary hammerdwarves kill Ogres (modded civ, larger than humans in iron plate armor) with base quality silver training weapons without taking a scratch. Champions are the shit, they can do things normal dwarves could never dream of. On the flipside, if you're using untrained recruits, high quality weapons can let them fight as though they're much more skilled than they are. It's always a balance.
2: Don't use marksdwarves. They're expensive to train up and odds are you don't have the metal to support a sustained marksdwarf defense. On top of that, if they take a bolt to the face you're out 600 successful shots, which takes more than a squad of goblins to refill (much more, even legendaries miss). You'll be looking at entire siege to train up a single legendary marksdwarf. Melee dwarves are much more powerful for the cost. However, a skilled bowyer or weaponsmith can make up for this, if you have excess bones raw marksdwarves with exceptional crossbows make a decent last line of defense.
3: Don't skimp on the crosstraining if you can afford it. Legendary wrestling adds a lot to any soldier. The additional dodge plus the massive experience gains giving them high stats makes them even more formidable. Letting them train with shields is even better, wrestlers often block punches, shield bashes, and grabs and trains up their shield user skill. It slows wrestling gain slightly, but it's a VERY good trade since the total avoidance gain is greater.