The Pats' pass-catching weapons are, by general acclaim, no better than league average. Henry is a solid TE, Smith was a disappointment. They lost one of the best pass-catching RBs in the world in James White. The WRs don't scare anyone, but Meyers and Bourne especially are solid, but it drops off considerably from there. In an ideal world, Bourne is a #2 and Meyers a possession #3, but they have to play more prominent roles given the rest of the talent.
Now all that being said, consider that they have a rookie QB. Not working with all-world receiving talent. Just average receiving talent at best. Not terrible. I don't believe for a second that the Pats have BAD talent at the skill positions. But it's no better than average.
And with that, with a rookie QB, the Pats finished with these rankings in terms of pass offense:
#14 in pass yds per game (226.9) - top 56% of NFL
#7 in pass yds per attempt (7.7) - top 78% of NFL
#5 in pass completion percentage (68.0%) - top 84% of NFL
#16 in pass TD (24) - top 50% of NFL
#15 in pass TD percentage (4.5) - top 53% of NFL
#12 in pass INT (12) - top 63% of NFL
#16 in pass INT percentage (2.4) - top 50% of NFL
#3 in sacks allowed (28) - pretty amazing for a rookie - top 91% of NFL
#9 in sack percentage (5.0%) - top 72% of NFL
#12 in passer rating (95.5) - top 63% of NFL
#9 in passer DVOA - top 72% of NFL
#12 in ANY/A (6.7) - top 63% of NFL
#13 in expected points contributed by the passing game (115.80) - top 59% of NFL
AVG rank: #11 - top 66% of NFL
So you look at all that, and there's no way that Mac Jones' 2021 season was anything worse than a top third QB in the league. Add in that he had average receiving talent around him (again, not BAD, but no better than average), and that's a pretty remarkable season for a true rookie.