That 3rd for 5th and Bennett rumor seems a bit off since its a bit much to trade away for him. I don't think that's something the Patriots would actually offer.
If it is, it highlights the VERY aggressive GM approach that Belichick has been adopting recently.
In the actual deal, the Eagles gave up a 5th
and WR Marcus Johnson in exchange for Bennett and a 7th. Johnson is a 6'1"/204 UDFA from 2017 who turns 24 in early August - speedy, athletic kid who turned in a reported 4.38/40 to go with a 37" vertical, an 11'3" broad jump, and 22 bench reps at his Texas pro day. He appeared in 10 games for the Eagles, catching 5 of 8 tgts for 45 yds. That's not a lot, but, considering how many other pass-catchers Wentz had at his disposal, the fact that Johnson saw the field and tgts at all may indicate some significant potential.
It's been rumored that the Seahawks will be letting Paul Richarson walk in free agency, so the inclusion of Johnson may have been as important to them as getting the 5th-rounder.
So, we don't know for certain whether or not the reports of the Pats "bidding" for Bennett are actually true. But we can still look at what the Pats had to offer and speculate that the Pats may have been willing to trade their 4th for Bennett, but that the Seahawks wanted Dorsett, too. If the Pats didn't want to lose Dorsett, maybe they then counter-proposed with their 3rd for Bennett and a 5th.
That probably seems like a higher cost than it really is, since the Pats 3rd is near the end of the round (#95) and the Seahawks 5th would have been near the beginning of the round (#141) - a trade back of 46 spots for Bennett. In terms of pick point-value, it would have been the equivalent of trading an early 4th-rounder.
I think that BB has always had a bit of a preference for building the roster with a good mix of NFL players with some proven chops - especially at certain positions (e.g., RB) and under certain circumstances (e.g., if the age/experience level of a positional unit skews very young) . As has been discussed elsewhere on the forum, that preference may have become stronger since the new CBA limited practices and, perhaps slowed the development of rookies somewhat.
In 2017, a very large percentage of DL snaps were, of necessity, given to two rookies - Butler and Wise. With the only Branch-replacement on the roster being 24-year-old Valentine and the possibility of adding yet another rookie draftee, the average age/experience level of the 2018 DL will skew even lower than it did in 2017. So, BB attempting to trade for a relatively affordable, accomplished veteran DL may have been a response to that situation, at least in part. Dropping back 46 spots in the draft to address that maybe doesn't seem all that aggressive, under those circumstances.