I suggest you go rewatch the Blizzcon reveal. It’s all explained there, but here’s a summary.
- Story missions. These will play like better versions of the Archives missions. Not intended to be highly replayable (Like the Archives missions)
- Hero missions. These are missions for every map in OW playable by every hero (Unlike story missions which have limited hero selections depending on the mission) These are intended to be “highly replayable”
- Progression systems: This includes the leveling system you’re talking about.
It came a couple patches ago: