Idiot, If we know what he did investigate, then we know what he did not!
He could have investigated several threads of evidence without results. (If you'd stuck around to receive a HS diploma that MIGHT have occurred to you.)
For example he could have looked at the Clinton campaign for signs of collusion/conspiracy with Russians.
Mueller had no conflict of interest, that's just moronic conspiracy theorizing by morons.
Your example of obstruction is hardly exhaustive as Mueller named 10 examples of obstruction of justice different from what you described.