I think that you're wrong, 1h stab is faster (it's ultra fast on horses) since weapons are faster themselves. Plus it's just different, you can't thrust anyone on clusterfuck. Plus onehander thrust is not as easy to chamber as 2hander. And it's completely wrong that onehanders have more powerful thrust than twohanders. There are two ways - buff twohander thrust or nerf onehanders.
I know you have a lot of experience with this game, but what you wrote here is just ridiculous. The 1h stab is still nothing compared to the 2h stab.
First: 1h weapons are not faster, animations make 2h swords faster except for the really fast 1h weapons without shield. (MW katana is still the fastest melee weapon of the game)
Second: 1h stab glances way more than 2h stab. If you take the weird stab animation of the 2h into account that's just bullshit, in close quarters the 1 stab should have more advantages.
Third: Who cares about the 1h stab on horses, it's not only rarely used it's also hard to hit anyone with it.
If anything buff 1h stab, the high pierce damage 1h swords are still underused (except for the italian sword which also has good cut damage and speed).
Also make the 2h swords 30+ pierce damage on thrust, but give them polearm stab animation. I say this even though I love to use the Great Sword on my 2h alt (and 70% of my attacks with this sword are stabs, because they are just so powerful).