I think the multiplayer is plenty accessible to players below Masters level. The matchmaking in SC2 was always more fair than the team based matchmaking games because 1v1 ELO systems are legitimately fair systems, compared to team ELO games where there's a lot more variance in skill.

>The beauty of League/Overwatch/PUBG/CSGO as an esport is the burden of game knowledge is relatively low comparatively.

This statement rings false for me - Overwatch and League (and DotA) are practically impossible for a novice or inexperienced player to follow because the number of unique characters and abilities is overwhelming. Contrast that with CS:GO or PUBG which is much more simple gunplay anyone can understand. In the middle of these extremes is Starcraft 2 where most of the in-game units are based off pre-existing sci-fi lore, and thus the function of the units is far more obvious to a novice spectator.

>RTS are essentially giant paper rock scissors games, but so fast paced it's really hard to get over the initial hump/learning curve, especially with as much micro across multiple groups as SC2 requires to get higher.

That's quite an oversimplification of the strategy required in Starcraft:Brood War or SC2. I'm sure other RTS are like this, but the ability to scout in those games creates a skillful back and forth with how a players build their tech/base/army and evolve their strategy throughout the match.