The point on a real scythe isn't sharp, it's rounded. Fantasy games have it pointed to look scarier.
I thought it was a given that we were talking about a scythe with a pointed tip. I've actually used a real scythe before; I realize that they're not as they're depicted in fantasy settings.
As far as the approach angle, it isn't uncommon, in fact it's very very predictable. And the swing is so wide you would never have to parry it in a traditional way. If someone swings a scythe at you in order to "pierce" you, and you step 4-6" back, it will miss. If they swing that wide, open swing, you can step into in and it would all be over.
It's uncommon in the context of the type of weapon that it is. If another weapon such as a spear or a sword approaches from that angle, they can be parried easily. Much of a skilled fighter's actions are conditioned reflexes, so while parrying might be a normal response, it can also be a fatal one.
As for your point that it only has to miss by a few inches, that's true of most weapons. I've already acknowledged that a scythe requires greater accuracy than other weapons and is a better theoretical weapon than a real-life one.
It would be terribly easy to step in on it. Parrying would never be necessary unless someone surprised you. And any weapon is effective with enough surprise.
That depends wholly on how quick and powerful the wielder is. Surprising people is relatively easy-- very easy with enough speed and minimal telegraphing. A well trained and conditioned human versus another human who is likely not conditioned against a scythe, well... the fact is, fighting against someone with a scythe is already a pretty big surprise on its own.
And a spear is the most efficient, effective piercing weapon in the history of martial combat. Every civilization, even today, has used a spear-like polearm as it's primary piercing weapon. It is a shining example of a tool build perfectly for a single purpose.
And as a result, it's a very predictable weapon. I don't question the spear's efficiency, though. But it's not capable of nearly as much piercing power as a scythe.
Your analogy isn't applicable. The golf ball doesn't move.
Fine. The golf balls are moving. My analogy becomes applicable again.
What if you miss? You are out of options while all other true martial weapons take that into consideration.
Virtually every weapon leaves you open if you miss, some more than others. Yes, the scythe is on the extreme end here, but it's not alone.
I am not arguing that the scythe is a good weapon in real life. It's a powerful weapon. But it doesn't take much power to kill a human, so the scythe ends up being overkill for what it does, and the situations it could be useful for don't present themselves in real life.
But hypothetically it's an extremely powerful weapon, and when you manipulate the speed, strength, and accuracy of a fictional character disproportionately to their evasiveness (par the course for fantasy, where missing is for flunkies), it becomes a very effective weapon. A similar effectiveness could apply to a human, but not an average one.