Bows are ridiculously overpowered compared to melee weapons, probably due to Strength bonues damage being applied to them (for whatever reason).

The further you can draw the bowstring back (without breaking the bow) the more force the arrow will strike with. That may not scale exactly the same as a melee weapon, but at least having the strength damage bonus is plausible.

There is one unique bow in DD, which you can get in the Dark Forest as a quest reward.

A high agility is good for a melee warrior. Sometimes getting the first hit in can make a significant difference in the outcome of a fight (especially when using the passive Stun skill), and missing a few times in a row with a strong opponent could mean death, or having to either retreat or burn though restoration potions.

On average throughout the game, most warriors characters will have 2 points in strength per level, 2 in agility and 1 in constitution. Of course that will vary, especially at the start of the game, based on weapon and armour requirements of what you find / buy, what bonuses your equipment has, and your playing style.

...Beyond Divinity (with my Death Knight being a pure melee tank and my character a mage summoner/archer)

I played a melee DK and crossbow archer hero; for the first part of act 1, though, crushing damage works better than piercing for many opponents (ie skeletons), so I had my hero use a club or walking stick most of the time. Playing again, I would make my hero the melee warrior and have the DK be a bow archer. The DK gains armour class as he levels, so doesn't need as much strength for equipment requirements; as a bow archer (or mage), he could neglect strength a bit in favour of agility (or intelligence). A crossbow is mostly strength based, so you would not be able to boost agility as much using one.

The math appendix of the Beyond Divinity Strategy Guide gives some general suggestions on stat point distribution.

Also, with bow/crossbow expertise skills, I only put a point or two into the damage and accuracy boosts, and a couple into Point Blank, but maxed Reload Time (gives a direct boost to Speed).

I didn't find bows/crossbows overpowered in BD, at least not sticking to normal arrows (in the original release arrows were much more expensive, so I saved up special arrows for later when I needed them, but didn't actually switch to power arrows until near the end of the game). I only used splitting arrows once, in a confined space with my hero and the act 1 summoning doll firing from different corners; the goup was very quickly cut down to just the boss, and I then switched to power arrows. The act 1 summoning doll is the only doll that can equip a ranged weapon (crossbow); most of the time I never bothered using it in battle (can not last long in a melee fight), but kept out of harm's way it can provide good support in tough battles.