I’d argue that it shows the opposite. That when it matters most, the US Congress can muster up a compromise and do so year after year.
This is like the least significant thing they could work together on. There are SO many more issues they could tackle together but won't.
Age may be an issue but I don’t think his experience should be in question.
Basically we're past the point of finding extremely qualified individuals as leaders, now it's much more of a popularity contest
Also, I’m not sure that this country has ever really selected leaders based on innate leadership potential (whatever that may be). Sometimes it selects for celebrity (I think GWB and Obama were arguably both in this bucket, despite traditional-ish political backgrounds), sometimes generals, sometimes Republican senators from Ohio.
But even for the presidents who turned out to be tremendously powerful leaders (Lincoln, FDR, LBJ), I’m not sure that was a deliberate choice by the voters ex ante (and obviously not in the case of LBJ).
As long as the elections keep on happening in a timely manner it's a "flaw" that can fix itself.