Celtics underachieved. They needed 4 HOFers in their early 30's just to get by 1 24 year old player who didn't have another all star or all NBA-er on the roster, and they only got 1 championship to show for it.
They then complained when he got with comparable talent in Miami and didn't face them alone. As we see, the series weren't close. When Paul Pierce played alone his teams were in the lottery every year and people felt sorry for him since he got stabbed.
Bron then makes KG and Pierce run to Kings County, New York in 2014 and bust their ass there too. He ends up winning just as many championships for Ray Allen and Rajon Rondo as Boston did.
LeBron has now beaten the Celtics in 4 consecutive playoff series and has the most playoff wins all time against the franchise. No other NBA player has that kind of success over them. He's the greatest opposing player in that franchises history and most sought after ticket over guys like Wilt, Kareem, Jordan, and Magic.