Edit: Basically, I'm an idiot. Misread the tooltip completely. Thanks to those below for not face crushing me. If forums mods see this feel free to erase it - I fully admit to being a waste of good oxygen this morning. I left the original post as punishment to myself and my ancestors.
I've seen a lot of very recent posts about MW and how great it's going to be for PvE. Even posts as recent as yesterday are talking about the instant cast benefits of MW in our DpS rotation.
Unless both Wowhead and MMO are incorrect - Maelstrom is no longer instant cast after 5 stacks. It only reduces the cast time (after stacking the maximum of five times) to 80% percent - which is basically crap.
I'm looking for some new info or explanation - I'm not trolling, I swear. I'm really curious about what people are thinking for our dps rotation.