I'd put Massive Attack on the main stage. They're immensely popular. The downside for RW is that Massive Attack prefers to perform at "green festivals," where a large percentage of attendees arrive by public or collective transport (buses). I'm afraid RW isn't green enough for them.
Last year, they were headlining Pohoda, but canceled that festival and several subsequent events (including Gent Jazz) a few days before the festival. I assume they'll reschedule those canceled festivals, starting with Pohoda (July 9-11).