Context matters, a lot. When my app logs a timeout against redis then my next question is "so what did redis do at the time, did it perhaps log something"?

Following your advice I'd either have to look in two places (redislog and syslog) or feed my syslog stream into redislog, to have everything end up in one place (redis).

Any sane person would do the latter. Under that premise, what's the benefit of having some apps log to redis directly when the syslog-stream also ends up in redis anyways?