Maybe all of the RPGs I've played the melee combat is weak on its own.
That IS usually the case, but Gothic 1 and 2 are definitely an exception. I thought Risen would be too when I started playing it, but while I am still enjoying the game itself, the combat system has been a letdown.
The problem with melee combat in RPGs stems from the problem with combat in general. Typical RPG combat is non-interactive to a large degree, meaning you do certain things regardless of what the enemy does, as if you are in two separate vacuums, and still have success. So in most RPGs, you can just spam something of choice (be it a fireball, a harm spell, a ranged weapon shot, a melee attack, etc) and deplete the enemy's HPs faster than they can yours, and you win. Obviously this is not how real combat works, where you instead have to read what the opponent is doing and react to them constantly. Now, some RPGs (those considered to have good combat systems, e.g. Baldur's Gate games or ToEE) do have some reactivity, for instance, if the enemy casts this protection spell, you cast this spell to remove it, or cast stoneskin to protect yourself from a melee attacker before casting offensive spells, and so on. However, this reactivity is very shallow, requiring no real effort and offering no real challenge beyond learning some basics. So you will ALWAYS cast stoneskin on your mage when in danger, ALWAYS cast Breach spell on enemy casters and so on. So in the big picture, you can say that the degree of reactivity is still pretty abysmal.
This is true of magic, archery and melee, but because magic has a lot more flavor (a ton of spells, flashy effects) it seems more interesting than melee, which only has a few basic attacks, and archery in some games might involve actual FPS-like aim and be more interesting that way.
The result is I'd always add magic, thievery, crafting or other skills to the pool to keep things interesting. Magic doesn't always supercede melee--in fact I don't remember it doing that in the RPGs I've played. So you don't think magic can add to melee in Risen?
I really hate mixing melee, archery or magic together. I am a purist, for a couple of reasons. One, I think one of the coolest things about RPGs is that you can carefully craft the kind of character that you want, a really cool character. So with that said, what character is the coolest? A master swordsman who dedicates his entire life to his craft, able to win a duel against anyone with his sword skills? A renowned archer who can put an arrow through the eye of a squirrel (on Trump's head possibly) from 40 feet away? A great archmage able to wield terrible powers to reshape the world? Or some jack-of-all trades douchebag who dabbles in everything? You decide. The other reason is, it's difficult enough to get a single system in an RPG right, be it melee combat, magic or archery. Once you start mixing them together, the result is usually an ugly mix of exploits and cheese. So stay pure my friends.