I firmly disagree. If this is the case then it really isn't an MVP award, it is a best player on the winning team award.
If your team is gutted of talent due to injury and you put up a performance for the ages to make it competitive you are the most valuable player in the series. Period. The situation matters too. If the team had been fully functional and still lost the same way with LeBron putting up the same numbers then I am fully on board, but you have to take it on a case by case basis or it isn't legitimate. Just call it a most valuable player on the winning team award and that's fine. But you can in no way say it reflected the best player in the series if the best player cannot win it. The regular season MVP is not always the best player on the best team. It is the player that most impact his team's success. You cannot argue that LeBron was not the most valuable of any player on either team in the series. Take him away and it is a 4 game series with 30 pt blow-outs. Take away Iggy and the Warriors still probably win. Take away even Curry and they still have a shot. Take away LeBron and there is no chance in hell that Cavs team wins even one game, maybe even not a single quarter.
I guess it depends on your definition of "most valuable".