1. That was not the primary justification at the time - it's only being floated now as a post-hoc rationalization. I believe McConnell may have mentioned it once or twice, but far more often, he (and every other Republican Senator) justified their positions based on the fact that it was "too close to the election." Lindsey Graham even used an identical situation as a hypothetical during a committee hearing and said that the hypothetical Republican president should not be allowed to choose a justice.
2. That's an absolutely ridiculous way of looking at things. What you're saying is, essentially, that the President has no power unless his party also holds the Senate. There are multiple problems with that idea. First, that's not how the government is meant to function. The Senate is a check on the Presidency, true, but it should not be able to nullify the President's actions except under extreme circumstances. There's a reason why a veto override takes a supermajority. Second, the Senate runs on 6-year terms, so it's composition does not fully represent the current political climate since only a subset of Senators are up for re-election at a time. The House, which runs on 2-year terms, would be a better proxy there. Third, the Senate does not proportionally represent the American people since every state has two Senators. A majority in the Senate does not necessarily represent a majority of the people in this country. Again, look to the House, which is distributed proportionally by population.