I wouldn't want to see spear stun to be implemented if it would also apply to regular spears. Spears in Bannerlord already have a very limited use and implementing more stuns would not be beneficial.
Implementing stun only for javelins = It's ok
Decreasing damage and speed = It's ok
Javelins currently aren't op weapons, but they are annoying to fight against and they are strong weapons in group fights thanks to their speed and high damage. In other words I don't mind Tw removing javelin melee mode. Only thing I hate is removing mechanics rather than balancing them.
Implementing stun only for javelins = It's ok
Decreasing damage and speed = It's ok
Javelins currently aren't op weapons, but they are annoying to fight against and they are strong weapons in group fights thanks to their speed and high damage. In other words I don't mind Tw removing javelin melee mode. Only thing I hate is removing mechanics rather than balancing them.