It seems that a spear can be defined as a single handed thrusting weapon that pierces with great force forward. In this definition, the spear in Valheim is consistent.

1) It does piercing damage, not slashing or blunt damage.

2) It is most capable at the point of attack.

3) It requires only one hand to use, allowing the other arm to use a shield.

I've had great success with spears, and it's my primary weapon. But I've used the atgier also, and have found success with the atgier as well. But they are two different weapons that require two different styles.

The speed at which I can attack with the spear is better than almost anything else in my arsenal, with the exception of maybe knives. In the time I spend attacking once with the atgier, I can get two strikes in with the spear.

That's conventional attacks, not specials. The spear doesn't have the AoE special like the atgier does. But, honestly, I'd rather have the versatility of the spear rather than that AoE special for most situations. And the versatility is in two respects. First, the spear allows me to carry a buckler for defense. Atgier doesn't provide for that. Second, I have the throwing option, which I use rarely, but if I need it, it's there. You can't throw an atgier.

You make a fair point about the attack having to be lined up rather perfectly on the spear in order for it to hit. Other weapons are a lot more forgiving. But I've spend so much time on the spear, I know how to move and when to strike. Spear technique in Valheim is a very active combat style, just like atgier is.

But the weapons are different. The techniques are different. Players can have good success with either one.