Hmmm. Not really. Yes, everything is a mix, but for applications, it very much is on the read-heavy side. Think about how many queries you have to do just to display an arbitrary page. You might, maybe, just maybe, net 2-3 writes vs. hundreds of reads. If that starts to balance out, or even flip, then you probably need to rethink your database as you start to exit traditional db usage patterns. But <30% writes is not write-heavy.