So, I just realized something. +20 weight difference enables a threshold called "power break tackles". What this means, I am currently unclear, but I currently run Bo who I do notice DBs bounce off of him or Bo easily pushes through for an extra 3-4 yards or so. Bettis weighs 256, Bo 227. This may be a legit difference maker against the meta of subbing safeties in at LB, although it's specific cases. Chancellor weighs 225. Simmons happens to be 237, exactly enough to disable the threshold. We then have to get down the list quite a bit to guys like Chinn, Dugger and Hamilton where the weight of Bettis makes a difference. Polamalu happens to weigh 207, so Bo weighs exactly enough to enable the threshold there. Obviously, an opponent who simply keeps LBs in might be able to stop the run a bit better, assuming the LBs can actually get there. And of course the game is fluky as hell, where any of this can get thrown out the window at random times anyway. I am debating where I'm at with this comparison at the moment, but let's get this out there for discussion purposes.
Edit - of relevant note, 88 Parsons has 87 speed and weighs 252, so if you need extra run defense you already got a decent guy for it assuming you watched MCS. I say decent because the hit power and pursuit rating leaves a bit to be desired, though at least tackling is a respectable 85.