Why is Rock weak to Water/Grass?

[Mr. Squirtle]

To get straight to the point, why is Rock weak to Water and Grass? I have looked at threads before (Yes, I did search before I posted) and the answer is usually: "Well, water and plants erode rocks over time." Yes, given thousands of years. Since a Pokemon battle is only a few minutes long, erosion isn't a legitimate reason for those types to be super effective against rock, imo. Is there some other reason I am missing? It seems like Game Freak just gave Rock and Ground the same two weaknesses just because they are similar, but this is the reason that everyone gets Rock and Ground confused in the first place.

If Rock didn't have Water and Grass weaknesses, however, would it possibly be too good, since it has good offensive typing and would only be weak to Steel, Fighting and Ground?

 

[LusoTrainer]

Water can break rocks, plant roots can do it as well and it doesn't take (thousands of) years for it to happen.

 

[Bellsprout]

I think the point is that in nature plants and water will eventually win over a rock. I get that a Pokemon battle isn't that long, but I think it's just the essence that these things occur.

Honestly I only got confused with rock and ground types in the beginning because they were typed together so often

 

[PlatinumDude]

It's simple: Water can erode rock over time, while plants can eventually use a rock's nutrients to sustain themselves.

 

[Bounsweet]

Well, the whole type weakness thing in general when it comes to Pokémon is pretty abstract for the sake of balance. Erosion is a pretty legit reason, when you think of how they made Fairy-types weak to Steel just because of the myths that fairies are allergic to iron, lol.

As far as Grass being super effective against Rock, I'd imagine it's because plant roots can break through rocks too and like PlatinumDude said they absorb the nutrients from it too.