That's not really true. A typical player can watch the replay of their losing match and see the proximate cause of the failure ("my army got blown up"), but looking at the game analytically to find the ultimate cause is/was much more difficult. The art of doing so was a regular feature of the Day[9] daily videos.
That complexity is part of what makes strategy games (real time or otherwise) compelling: seemingly simple choices or optimizations compound into a much larger advantage later on. However, those small-scale advantages are rarely highlighted by the game itself as important, and optimization usually asks a lot of the players.
Also arranged teams have a very strong advantage over random teams, you can really punch above your weight if your teammates understand how to support you.