8/10 uses of redis I have encountered in the world were people using it as a slower memcached.
1/10 are using it as a hope-for-the-best "queue" instead of rabbitmq, which is bullet-proof.
The last 1/10 actually use it as a novel "database" but every one of those instances also has mysql or postgres, rendering it completely redundant.
Redis itself was, for a while, a massive open security hole when the above people would put it on the open internet, where it would to quite useful to hackers as a free lua program runner.
Isn't it good for building and querying custom indexes? Doing that with mysql or postgres is very difficult or impossible depending on hosting solution.
Or would you still prefer to build on top of memcached?
VIEWS and MATERIALIZED VIEWS probably are a better version of what you are talking about?
If you are running slow queries and caching them into into a k:v store you can just do that with a TEMPORARY TABLE - sql databases are absurdly fast k:v stores.
There are valid use cases for redis in its novel types and things but my comment was trying to express that seeing that usage, in my real life experience, has been rare.