You always see athletes that focus the 100/200, or 200/400, but rarely just the 200M.
"Focusing on the 200M" doesn't make any sense. It exists either because it gives the 100M losers a chance to win another race, or to give the 400 runners a bit of speed work after they run their main race prior.
If you excel at the 200M but refuse to run any other race, you are wasting talent on a more significant event.
A 21.00 200M runner should be able to run either a 46.00 400M or a ~10.3x 100M
The mix of top speed and speed endurance in the 200M is a byproduct of either the 100M athlete or the 400M athlete.
It is, and always will be a secondary event.