I think an argument can be made for this just over the past couple of years. As you say, age (and injuries) are catching up to him. He has played manyyyy more games than MJ has in the league, against, arguably much better competition (everyone is faster and stronger these days so you have to work twice as hard to stay ahead). Having said that... I don't think this argument holds up during his prime and first ~15-16 seasons in the NBA.
I think it does hold up for his entire career. If I may cite an example in his first run in Cleveland. He first finals loss to the spurs, on twitter he says something to the extent of "I'm going to wake up and still be LeBron James, you all will wake up and go back to your miserable little lives..." That's not the mindset of a competitor imo. With that being said, I think there's an argument about different times now and then from a social media aspect.
Also, when it comes to the competition, I think the "bigger, faster, stronger" is very accurate but there's two things that I would counter with.
A.) The skill gap is not only hard to identify, but to measure the differences between 1 and 50th from multiple eras would be almost impossible. Because of that, I can't really take the "competition" argument seriously. I would only say that the level of respect, reverence, and downright fear that players attribute to playing against MJ is completely different from those you hear when discussing Bron. People definitely respect Bron, but they hold him in the same regard as they held MJ.
B.) As the NBA transitions from million dollar, to multi-million dollar, to now a billion dollar industry, the effort and research that goes into health and fitness will grow exponentially thus making the comparison of players even more difficult. Comparing Bron to Jordan physically is simply solved by saying look at the wealth of information regarding fitness and health now from that time. That doesn't make Bron "better" than MJ, it just means that his resources are more plentiful.
Lastly, I'm enjoying this debate, but I'd prefer we have it in a different thread if we want to continue. I don't want to steal the
@Windwalker thunder with all that he has going on.