Seth Alexander, who runs the Massachusetts Institute of Technology’s endowment, has produced long-term returns that beat many of his rivals. Yet, he was compensated less. Among the 10 wealthiest private schools, MIT bested eight of nine endowments in the five years through June 2017. Alexander received a $2.1 million pay package in 2016, ranking him at the bottom. The 10 had an average $4.3 million package, according to data compiled by Bloomberg using the schools’ most recent tax filings. The schools either declined to comment or didn’t respond to requests for comment.