It's always a blend of both theories. Especially for a team with as many problem areas as we have.
This is precisely the answer, IMHO.
We're not going to take a K, P, KR, or LS simply because they're the best at their position. Certain positions have more value. For instance, QB has the highest value, but when a team has one in his prime, that premium for the position disappears. Similarly, LT, CB and pass rusher are the typically highest valued positions after QB. We had an aging, injury-prone and expensive LT with very few years left, so we drafted where BPA met value and still a position of need with Laremy Tunsil. We drafted a combo of BPA, value and a position of need when we drafted Xavien Howard, but we needed to trade up to get to the spot where those converged. And there seems to be evidence that we may have been going after someone else (UCLA LB Myles Jack?) when we decided to trade up, but he was drafted by another team (Jacksonville?) before we selected.
Regardless, I think those two picks were arguably both BPA and need picks. From the Dolphins draft board, we definitely got value from those guys. From a talent evaluation perspective, both of those guys validated their ability as rookies. We can argue that need seemed to overshadow BPA with the picks of Drake and Caroo. But in each case, it's not clear whether that perceived need was in fact an actual need, as we also had Ajayi and Parker.
Looking at the rest of the picks it does seem like their positions were specified with the selections of DB Lucas, TE Duarte, and returner/WR Grant. No disrespect intended for those players, but they seem like they were chosen to fill specific roles in Gase's offense. While I was never a fan of Duarte and definitely disliked Lucas, I was and remain a fan of Jakeem Grant.
Gase wanted to surround Tannehill with talent that suited Gase's system and Tannehill's style. I expected to see that same logic applied to the OL this free agency, but it was not. Maybe that means we draft for need by taking OL early?
Despite the propaganda, zero teams draft strictly BPA. But, nobody in personnel will ever admit it, because then their bosses think they're intentionally drafting worse players, and they get fired. But reality is that they know they're not picking a group of players, but rather picking a team. For the team to succeed, those players must fit the coaching staff's ability to utilize them and complement the rest of the team. Simply drafting 7 QB's every year is sheer stupidity, so it is rare for a team to draft 2 players from the same position, and extremely rare to draft more than 2 from the same position in a given year. Drafting LB in round 1 probably guarantees that we don't look at another LB until round 5 at the earliest. Drafting a CB in round 1 is the same situation, but that doesn't mean we wouldn't come back and draft a S in the 3rd.
Need always plays a major role in every selection. But at the end of the day, getting great players trumps getting solid players at a position of need. When it's close, the war rooms will have arguments for need vs. value. Nobody takes ownership for their argument, because if they're wrong, they're fired.