That said, I don't particularly like how 5e handled the rapier. I don't particularly like how bland all the weapons are. If I designed the rapier, as a reaction you'd be able to counter-attack an enemy that missed you by 5 or more. Of course, if I designed the whip you'd be able to spend a reaction to try to trip or disarm an enemy on a successful attack roll.
5e's ethos seems to be to empower the character rather than weapon minutiae. Riposting/counter hitting isn't something solely performed by rapiers, so it would make more sense to make that a feat in the same vein as Defensive Duellist so that someone trained to be able to do this could choose whatever weapon they want. If you make it a weapon property of the rapier, then someone who wants to be able to do this is forced to use a rapier.
I have to agree in sentiment: I wish every weapon had particular strengths and weaknesses so that there was no such thing as an optimal choice.
I believe that this would actually have the opposite effect: Currently players have access to a range of weapons with the occasional minor trade-off of damage. If every weapon had more specific strengths and weaknesses it would still give an 'optimal' choice: the weapon with the property that the player wants to use.
This is my only gripe with 5th edition. Simplifying the rules is fine. But I wish they had found a way to have it be simple, AND also have armor and damage types matter more. What is the point of a weapon dealing piercing damage, if piercing damage has no effect on armor?
5e really isn't granular enough to deal with that sort of detail though. For example: rapiers are pretty ineffective against most armour, yet war picks and daggers were a favourite to use against even the strongest armours. They all do piercing damage.
Damage type effectiveness in 5e is limited to things like skeletons, rather than fall down the rabbit hole of chasing after ever-increasing realism.
Same with spears. I think a throwing spear should be able to disable an opponent's shield if it is blocked by the opponent. And maybe a whip should be allowed to strike multiple opponents, to some what balance its pathetic damage.
Messing with shields was a function of one specific design of javelin, used in mass combat. It probably doesn't translate well to the very short, individual combat that adventurers tend to engage in.
Whips don't have pathetic damage for balance. They have pathetic damage because whips are very bad at killing people compared to other weapons. A character using a whip is probably using it for its unique properties (only finesse, reach weapon for example) or because they are doing other things (such as swinging from beams) rather than primarily killing people with it.
(and in 3.5 there were even feats to use the whip to do cool things, such as using it as a grappling hook.)
The issue there is that the existence of a feat that allows you to use a whip to catch on to things implies that you can't do that without the feat.
In 5e, if you want to use a whip to snag a beam to swing across a pit, you just tell your DM. They will make a ruling, probably giving you a bonus or advantage to your check rather than asking "do you have the feat".
