Kobe and Duncan were far better players on far better teams by Bron's 2nd title than Magic/Isiah were by MJ's 2nd title, but that's not even the point.
The point of saying that Magic/Isiah/Bird all declined is that NO ONE filled the gap. There were NO comparable superstars on strong teams in the 1990s other than MJ. Bron was facing KD with an elite Thunder squad, Duncan with an elite Spurs squad, and Steph with an elite Warriors squad all the way through his prime. You could even count Dirk and the Mavs since Dirk is an all-time top-20 player in his prime and the 2011 Mavs were a better team than anyone MJ beat. There wasn't a single year from 2011 to 2018 where a really, really good team wasn't standing between Bron's team and the title.
Who the hell was that for MJ? In 1991, the Pistons, Celtics, and Lakers were all injured as fukk and stood no chance (Laker injuries didn't hit until the Finals, when Worthy and Scott both got nailed right at the beginning). All the other years, the teams he beat were flashes in the pan, inferior stars leading inferior lineups. If MJ's 92/93 opponents were any good, why couldn't they win anything before 92 or after 93? If the 96-98 squads were any good, then why didn't any of them do anything in 94/95 or 99/00? None of those teams did anything before MJ's runs, none of those teams did anything after MJ's runs, and none of those teams did anything in the years between.
Outside of the Lakers (who hadn't won in 3 years and got 2 of their top 3 hurt for the Finals), MJ didn't beat a single historically relevant team or star during his runs. The best he could say is Barkley and Malone, and both of them are famous for being playoff losers. If Jordan wasn't around, the 90s would have been no different than the fukking 70s, a bunch of mediocre-ass squads taking turns in Finals that no one would have remembered.
Every player MJ beat in the 1990s came into the NBA around the same time MJ did and hit their primes around the sametime MJ did. These are all time great players who were his peers. Ewing, Barkley, Malone, Stockton, Hakeem, Drexler, Robinson, and then the baby Hall Of Famers like O’Neal, Hardaway(had he stayed healthy), GP. MJ retired the 1980s players when he finally hit his stride and hit his prime years, and then went on to dominate his peers when they all hit their stride and hit their prime years. The 2011 Heat, were favorites becaue of the talent gap of the 3 stars. As well as Dirk played, there wasn’t a single number 2 on that Mavericks team that was as good as Dwyane Wade, and there wasn’t a single 3rd option as good as Bosh was. Everyone gives them props for beating the lakers and baby thunder that season en route to Miami, but that lakers squad didn’t do anything of note after that season and Kobe’s decline was already in swing the very next season. He was 15yrs in by that point. KD wouldn’t win his first title until 2017, so OKC wasn’t ready. As good of a run as that was, Miami had the talent advantage and still managed to take Dallas to 6 inspite of LeBron not playing like himself. That was a solid Mavs team, but the lore of this Mavs team is mostly lies in retrospect of them beating the Big 3, moreso than them being viewed as the favorites in real time. Miami should’ve beat them. Game 2 was in their grasp. 2011 is a blunder.
Who were the juggernauts who were going to oppose Miami in 2012? Golden State hasn’t made the leap yet. Dallas was on the down swing. Kobe was aging and the lakers run was over. Derrick Rose injury prone career was starting to show its self. Literally no one was standing between Big 3 Miami and the title. Boston was on the down swing. They were in their “old guy but still good” phase, much like Detroit, LA and Boston was when MJ hit his stride in 90-91. They literally blew it up the next season after Miami beat them in 2012. OKC was still the baby thunder. As good of run as they had, they weren’t a serious juggernaut against a more experienced Heat roster. Even harden being 6th man of the year, he underachieved in the finals that season. So looking at LeBrons first title run, despite Timmy D and Kobe still being very good players, the teams LeBron actually face en route to the title weren’t juggernauts and there really wasn’t a “favorite” team to upset Miami that post season. It was Miamis for the taken from the first game in December from the lockout, when Miami blew Dallas out.
2013 is when you could say the post season got a little shaky for Miami. But even then, this was the season Miami added some key pieces and got even deeper and went on the record win streak in the regular season. So even then, the 2013 Heat team was one of the better supporting casts surrounding LeBron. Even though Ray Allen was past his prime, he was still regarded as the best 3 point shooter in the NBA. And he was added to Miami literally just to shoot wide open 3s. Nevertheless, Indiana and San Antonio were two solid teams that pushed Miami to the brink. But still, there were no true juggernauts that had a talent advantage over Miami to say that LeBron had faced tougher teams than MJ. 2016, 2017, 2018 Golden State is when you start to get to “LeBron overachieved” status. In Miami, LeBron more times than not had the superior supporting cast, really until 2014 when wade collapsed and the depth didn’t present it’s self.