Let's talk about the ability of ranged units to go wherever they want without care of needing allies to support them and offer protection. Archers move into unsupported positions on the flanks where they can shoot into the flanks of the enemy, and it's a big part of the imbalance problem.
Against cavalry, xbows aren't the problem.
On my horse, I stay away from loaded xbows. They can point it at me all they want while I stay away and look to dodge. They are safe from me as long as they hold the shot, so it's a fair stalemate. If they shoot, they are open to melee combat. This means that a cav can stop a lone xbow from shooting anymore, which is probably why you don't see too many xbows running around alone. They need protection. If they actually have allied support protecting them, they can shoot and reload freely.
Throwers aren't the problem.
With throwers, I'm forced to keep my distance as long as they are aware of me, and they can't hit me from long distance. Pretty balanced. They could go where they want unprotected (like a skirmisher), but they need to get close to actually be a threat. It's a fair balance.
Archers, on the other hand, can be all alone just fine, even against cav.
They have no problem firing at will. They can just shoot rapid fire, and those shots are accurate and fast traveling even at quite long range. Plus those shots seem just as powerful as throwing javelins, and even more powerful than xbows (assuming they've put a lot into PD).
Alright, so there is no stalemate. You gotta bite the bullet and charge, take lots of damage, hope you have something with more health and armor than a rouncey/palfrey (since they routinely get 1-shotted), and then shield up before you attack since they'll just stun you with a shot as you approach. Fine. It's powerful stuff.
But here's the kicker. Cav still can't force the archer to stop shooting and switch into melee. You've gotten close, but they can still keep shooting if they are decent enough to keep sidestepping while firing, or they can use a melee weapon for defense and then switch back to the bow to get a shot off after the cav passes and is trying to turn around. We're talking about a lone archer or 2, standing off somewhere without support, unafraid of infantry who they can just kite, and unafraid of cav who they can keep at bay while they cut them down.
So how about this?
Make archers unable to draw and shoot while moving. They must be standing still to draw and shoot. Now if they are all alone somewhere without support, at least a cav can force them into a melee battle and not just get shot up at point blank range. This would help a little to discourage archers from being untouchable loners that surround enemy infantry from all different angles.
This also means it'd be harder for them to shoot while kiting infantry and doing any kind of point-blank shooting versus opponents. Plus they won't be dodging arrows while drawing the bow and will make themselves vulnerable to other archers while trying to shoot. So the biggest threat to archers may be other archers. And it'd finally give xbows something that archers wouldn't have, the ability to move and shoot.