Nothing is impossible is a stupid statement. There are plenty of things that are impossible.
And yes, it is impossible to make a stat system that does everything. You just aren't using your imagination if you think it is possible.
Like my stat system on my server has "meleeRange" and "distanceRange" in it, which will change the range that your distance weapons and melee weapons can hit.
Guess what, this stat can be on rings, armors, helmets, shields, anything.
Tada, you need either source edits, or making a script for every single weapon in weapons.xml for this to work.
So lets say you DO add this functionality to your stat system. You have "meleeRange" and "distanceRange".
Then a new person downloads your stat system and says "hmm I want Elevation stat, that increases your elevation so players and creatures can levitate around."
So they go into TFS source and OTClient source and make a new Elevation ability, where players can float above the ground when they have the elevation stat, the higher the stat, the higher they float.
Tada, you don't have that functionality, and even if you "added" it, they'd need to use YOUR OTClient and TFS to do it. But what if a player already has their own OTClient and TFS? I guess you could have a tutorial of how to add it.
Then a new person would download your OTClient and TFS and Stat System and think to them self, "Hmm, this stat system is great, but I want a stat so when you eat food, it fills you up faster, and a stat that makes potions work better, and a stat that makes it so when you get hit, you urinate on the attacker and it does poison damage, and a stat that makes it so your weapon has a higher chance to cause bleed damage, and a stat that makes it so when you are healed there is a chance for a rainbow appear above my character and it heals other players around me, and a stat that makes it so when I die, rats will come and eat my dead body before other people can loot it (higher the stat, the more rats that come), and a stat that makes it so every time I attack, it posts a new post on THIS thread showing a new stat you don't have (the higher the stat, the longer the forum post would be).
I'm saying custom servers, (at least good ones) require thought, and you can't just copy and paste a bunch of people's ideas and say it's good, you WILL have to do your own custom work, with your own custom systems, and maybe they can use your stat system as a base, but it WILL NOT do everything they need it to do 99% of the time.