Right. Got it. I am now going to answer those line by line.
1) While all three of those were reasons, the main one was that he simply did not fit the scheme. Brown is a poor man's Dwight Freeny with less explosion, and less agility. He is very tight in the hips, which makes him near impossible to plug in at linebacker. A linebacker is a linebacker is a linebacker. Simply because the defense evolved out of the 52 and the position evolved out of ends does not make the requirements the same as an undersized end.
I wouldnt call him a poor mans Dwight Freeny yet because none of use have seen him play in the NFL yet. Players evolve as they get to the NFL, hopefully every player that we draft learns new things and becomes a better player than before. As far as "the system goes, find a player coming out of college that "fits the system" over the past few years.
2) I don't know about a massive influx. Last time I checked, there hasn't been an expansion in a few years. A shift? Maybe, but that's the way the game moves and evolves. The thing that you can't seem to grasp is that just because a defense is a 34 doesn't mean the defenses are the same, nor are they remotely similar. There's respective permutations, hybrids, strategies, and philosophies for each brand of the defense. Ranging from the purest (albeit troglodytic and deeply flawed) 1-gap downhill schemes (ie, San Diego, Dallas) to the purest 2-gap reactionary scheme (Cleveland). The players you need for each scheme are different. In the NE scheme (somewhere between LeBeau and Mangini) the players have a highly complex set of requirements. Rushing the passer is only a small fraction of what the players are asked to do. In fact, one could argue that the ability to run with and cover TE's is the primary requirement.
I used the word influx because the 3-4 use to be an exclusive club at one point, BB himself said that when he got to NE it was only them and Pitt that were running the 3-4( I belive) Yes diffrent 3-4 D's exist, I know that Rex Ryans 3-4 is more aggresive than ours but that does not mean that the players that play in the diffrent 3-4s cannot adapt to our 3-4 (Look at Adalius Thomas comming from Baltimore) I also have to disagree that rushing the passer is only a small fraction because if you watch a game from last year or any year from when BB arrived I promise you that you will see the OLB Rushing the Passer more than dropping into coverage on passing plays.
Players in college don't play in the NE 34. There is no other version of it in the major 1a conferences. It is simply too complicated to effectively implement on the collegiate level. Keep in mind that these are student athletes who don't have as much time as professionals to grasp these concepts and learn their responsibilities at such a high level. Accordingly, it is a crap shoot in tape evaluation. Tape evaluation is the single most valuable aspect of the draft, and is roughly 85% of a team's decision. I know this because I have college teammates currently playing in the NFL. Downhill 34 schemes are far easier to scout for, because you are essentially taking a defensive end and moving him off the line three yards in a two point. It's the same position in that scheme as it is in college.
To suggest that the only way to get an outstanding 34 OLB is to take a player in the top 10 is...well....frankly ******ed. The Patriots wouldn't have enough tape on the player to make a risk mitigating evaluation. Instead, they chose to identify potential fits available in the later rounds or in free agency. This is obviously in the interest of risk management and BPA. They only recently have begun looking for the fits at the position. We (fans) currently have no idea how any of these players are going to pan out.
OF course you can get an outstanding 3-4 OLB from other rounds in the draft but what I am saying is your not going to get the "perfect OLB" in this day in age with so many teams now running a variation of the 3-4. Free Agency is another option as so many OLB are projected to be Free agents after this season, but will the Pats fork over the money with all of their own free agents?