I found Flux to be awesome in that it allowed me to express queries that wouldn’t be expressible at all with promQL or SQL. Yes, you could write down a query that was extremely slow, but I rarely hit those cases.
Not that I’m going to miss it very much; in fact them going back to SQL in IOx immediately put brakes on my effort not only to further learn the language, but also any desire to write any further dashboards and left me feeling I wasted a bunch of time learning it as much as I've done up to that point. I just hope they don’t end up going back to Flux again in 4.0.