The point in SC2 is that it's so fragile that very often not the better player wins, but the winner is determined by luck (best example: this close group). The skill ceiling in SC2 is reached by all the top players, and minor mistakes, random stuff like scouting luck or build order luck decide the games and often whole careers.
Flash has yet to improve, yes, but it's not his fault alone. How many "upsets" have been happening in the last months of SC2? It's the common thing in SC2 to happen.
A fact is: A top SC2 player can often lose to a worse player. Substantially more often than for example in Chess or also Starcraft:Broodwar.
Look at WCS EU. Three seasons and three times almost all new RO8 players. It's like shuffeling, luck and minor things.
For the best player to mostly win there needs to be a higher skill ceiling and more possibilities to come back. It's just not there yet in SC2 gameplay-wise - as all the results have shown the last year - and probably will never be, according to Blizzard.
And that all is in my opinion the prime reason for SC2's decline. The crowd wants heroes winning, it wants them to do things that normal players never could do (like thinking 8 moves ahead in chess or doing perfect storms in broodwar), and it wants comebacks to happen. All those things are rather seldom in SC2. But why am I writing this... 3 years ago we told Blizzard exactly this and nothing changed.