Remember "reinventing government"?
I would say that, like the President, the time period dictates the difficulty of governing and in calm times - less is needed. I would argue that the Obama years were among the most challenging in our history. Obama, with a very experienced VP, delegated some very big issues to the VP to lead on.
These things included monitoring the various parts of the stimulus package. It was a very complex response to preventing the economy falling off the cliff. He also took the lead on Iraq in the first term. (That had a more mixed result. He did get us out before the election, which was a political plus and it was not entirely by choice, but dictated by the lack of a SOFA agreement that he tried to negotiate. ) I would argue that - other than healthcare - these were the top two issues of the first term. Obama had a very strong cabinet both terms. If Obama did have strong faith in Biden, there were other people he could have assigned both of these tasks to. In addition, to those specific issues, it is also clear that Biden was Obama's top surrogate with the House and especially the Senate.
Obviously, this argument could likely have been stronger had it been made in 2016. I wonder if on some level this argument is harder to make as Obama clearly strongly favored HRC as his successor over Biden.