The #gameplay-and-training channel consensus seems to be that you can get to ~1.8k by just executing the basic strategy for each map very efficiently.
I.e. if you are just very good at spamming tanks on ladder or really efficient with your eco/build in defensive team games, you'll reach 1.8k in them.
Beyond that it seems to be a combination of a lot of things:
- Map awareness and gamesense allowing you to accurately know how the game is going and make the correct decision based on that.
- Adaptability seems to be a huge one, allowing you to not only choose the correct strategy based on the situation but also be able to execute it well.
- "APM", so that you can micro a bomber, sent a raid and macro on the back end, all pretty much perfectly. This also allows you to either deal a lot of damage with little mass investment, or trade your apm for your opponent's, which is a good trade because you presumably have more. Apm probably matters a lot more on 20x20 ladder, but as a certified Setoner(TM) I wouldn't know
- "Teamsense": being able to judge what your allies are good/bad at, adjusting your strategy accordingly.
- Being comfortable in unconventional situations: Ever got a 2nd or 3rd base in a fullshare game, didn't know what to do and suddenly had a full mass bar? Yeah, that shouldn't happen.
- Being even more efficient: While a 1.8k is decent at whatever they do, there are still huge improvements possible. The 2.5ks we have can talk to their stream, while also shitposting on the ingame chat and still have better eco and micro than I do in my tryhard sandbox games. Also even a couple percent improvement in whatever you do actually matters quite a lot due to the exponential nature of the game.
- Being even better prepared: Many of the "serious" BOs go to straight up absurd lengths of optimizations, e.g. delaying a single pgen by 10 seconds at min 5.
In short: It doesn't seem to be one big thing but many small things to improve from 1.8k onward.
Would be interesting to hear what our resident >2.2k players think though.