I don't favor the notion that Sheeran was there that day. It's true he was near Detriot but the evidence suggests that he got in Detriot on the 31, the day after the muder. There is a great breakdown of that evidence on the website called lawfare (by Goldsmith: https://www.lawfaremedia.org/article/are-claims-new-film-irishman-true).
It is true that Hoffa would have gotten in a car with Sheeran but I don't think he did that day.

The most plausible theory is that Billy Giacalone was certainty there to pick him up. He was accompanied by Quasarano and/or Vitale. There is a strong possibility that Tony Pallazolo was there or had very good first-hand knowledge of the crime, possibly because he was part of the disposal team. This is because Pallazolo was caught on a wrireap speaking about the disposal.

One last thing: There is a lawyer who worked for the Detroit mafia, Paul Zibursky, who, in a recent interview with Scott Burnstein, called Billy Giacalone "the guy who whacked Hoffa". This seems plausible to me since I contend Giacalone was there. Whether he did or not, we will never know. What is clear is that one of the above mobsters did it.