Redis doesn't necessarily have to be used as a cache. Streams, for example, make it a great message queue; but a single-node message queue is a single point of failure and thus not viable for many setups.
That you do. Until you realise that there is only a single writer in that scenario, it doesn’t address any sharding concerns, you need to use compatible clients that opt into the sentinel protocol, during failover you’ll see client errors… there’s lots of room for improvement on redis HA.
With the amount of problems I had using Redis Sentinel, I really wish there was another way. On multiple occasions, with completely different deployments, it got itself into a non-repairable state where the only option was to drop it and setup the replicas manually. I was hoping someone would do a Patroni-like project for Redis, but I've not found it yet. I've moved all persistent data to PostgreSQL and use a number of Valkeys behind Envoy proxy as a cache.
I suggest you to take a look at rdsync (https://github.com/yandex/rdsync), exactly what you want: Patroni-like high-availability tool for Valkey/Redis. Uses ZooKeeper for external coordination. We use it in our large deployment and with a couple patches you will forged about the need to take manual actions to resolve broken states.
To be honest - at any scale, this really does help me not wake up at night to fix broken states by hand as sometimes on-call engineer. Although note that rdsync is mainly for Valkey up to 9.1, there were Redis patches for 7.2 (last BSD version).