I'm trying to show you that this is a lorefull rule change if you eree going to give humans a weapon profincy polarms makes the most sense.
It really would not. How polearms are used in combat have very little to do with how farmers use a scythe, which by the by is not by any stretch of anyone's imagination a polearm. And there's no sensible argument that I can think of that being familiar with a scythe somehow teaches you how to use a polearm.
Also keep in mind that a war scythe really isn't a scythe. It is named so because it has a curved blade, like a scythe, and the cutting edge is on the inside of the curve, like a scythe. That's it. You cannot make a reasonable weapon out of a scythe because the blade just isn't made for it. Sure, you could injure people but you'll probably also break the blade or it might get stuck or it might just glance off the first bit of armor it hits.
If humans were to have a basic proficiency, it should probably be basic spears, which I believe is the most common weapon in human history, since it is so simple to make. But even that wouldn't be right, because learning to use a spear properly takes time and effort and investment. It sure isn't something that all people of any society just know how to do.
My dude polarms evolved directly from farming equipment.
Weapons like the bill were almost 1 for 1 for their agricultural counterpart.
But I'm not sure why you are bringing up the practicality of scythes, we we know they are thing in the forgotten relms reguardless, see Myrkull's nighriders
https://forgottenrealms.fandom.com/wiki/Night_rider?file=Servants_of_Myrkul.jpgMy dude, polearms almost certainly evolved from farming equipment but that does not make farming equipment and polearms the same thing, and it certainly does not make farm use of farm equipment equal to war use of derived weaponry. Rakes and shovels and such are also not polearms, even though they too have a metal head mounted on a pole.
And as for Myrkul's nightriders, would you care to tell me the 5E stats of those scythes? Leaving that aside, you are surely not suggesting that we should think of a hand-wielded lawnmower, essentially a large gardening tool, as a polearm, a tool of warfare, just because it might at one time have been suggested by something published by WOTC? Some application of common sense is always a good idea.
A "scythe of wounding" is one of those things that sounds badass, might even look badass if depicted the right way, but makes as much sense as bladed nunchucks. Clearly someone somewhere misunderstood what a scythe was or plain did not care because of the cool-factor.
Whatever it is, the idea that a farmer's use of a scythe somehow translates into everybody knowing how to use polearms effectively is plainly incapable of holding water.
