"Hillary would surely have succeeded on competence in any other election, no?"
No. She would have lost easily much earlier to any other sensible candidate - in many ways Trump was lucky his contender was Ms. Clinton.
Why the Democratic Party had only one candidate (but an outsider with no chances like Sanders)? She would have lost the nomination too against any sensible Democratic candidate - so "somebody" ensured there were none - strange, because there was no president seeking for a second mandate.
Why Clinton didn't keep the Secretary of State role? Was it a cunning calculation to stay away from any current administration mistake? Was her stint at that place a show of competence, or not? Lots of mistakes, in the US foreign policies, in those years. Obama's ones, or Clinton's ones? Having been a US lawyer and a President's wife doesn't endow you with magical foreign matters knowledge - if's a field that requires of lot of time actually spent abroad and on the specific matter.
As a Senator, did she show much competence?
Someone, I don't remember who exactly now, wrote that Ms. Clinton was a very weak candidate, under many aspects. She was kept afloat by Trump being a real risk, but it wasn't enough.