It's definitely sad to see a LB without athleticism these days. But honestly, just being athletic isn't enough. I still maintain that LB is the most instinctive position on the football field. It requires constantly reading signals all around you and knowing tendencies. Athletics only really comes in at the point you figure out what's going on around you. If you take a tick to process that, you become a Channing Crowder type, with all-world physical ability but average to below average production. He goes from point A to point B in 1.5 seconds, but it takes him 0.5 more to figure out that he needs to get to point B, so his total travel time ends up being 2.0 seconds ... which negates most of his athleticism.
Guys like Zach Thomas looked fast because they figured stuff out before everyone else. Their eyes took in information all across the field, not just in front of them, but also wide peripheral vision. Then they processed that information lightning quick and matched it up with the patterns they had studied on film. So, they concluded that there was a 75% chance that they'd need to get to point B before it even happened, so they'd cheat and take 1 step in that direction. Then when the play took a half-beat more the likelihood went up to 90% that they were going to point B, they took off, arriving way before they were expected and royally pizzing off the offensive players who couldn't figure out why this small slow guy kept beating them to their spot. When you pair that kind of eyes and mind with elite athletic skills, you get guys like Patrick Willis. And honestly, Anthony's athletic ability is probably ahead of Willis' but he's not even in the race with vision and processing.
Alas, our scouting department keeps thinking that foot talent is 90% of what they're looking for in a player. Speed, quickness ... sure, it's very important ... but so is technique. The Patriots prioritize technique ... we never do.