That's the right description about stable coins but it's not that many of them at all. There are actually a few of them that are popular.
Does anyone invest in stablecoin? I have never heard although it's possible to get a little profit sometimes. However, people use stablecoin to fix their profit or stop their loss by converting their coin to stable. There's no other use of stablecoin then this.
Probably a newbie that doesn't understand it if he/she buys it, they will think that they have invested on cryptocurrencies.
You are right, sometimes there are few people who have never or lacked research into the coins that they will invest in and think about if they buy at a good price for long-term even though all of that is wrong. There are still many newbie with minimal information about stable coins.