Bryan Thomas does some things well on the field. He is very capable of setting the edge, getting off blocks, and playing the run well. He is also pretty fluid is coverage. Opponents only threw at him 13 times in the 129 times he dropped and averaged 3.3 yards per attempt.
The problem comes with what Thomas does not do. That is rush the passer. Outside linebackers in the 3-4 are supposed to be athletic enough to win the edge. They are supposed to use leverage to fight off blocks. They are supposed to be playmakers. If a 3-4 team has pass rushing issues, it is usually due to the outside linebackers. Thomas does none of the things mentioned consistently and has not aside from his 8.5 sack contract year.
I know he led the Jets in sacks, but many of those were coverage sacks that were caused more by the secondary than him. It does not say much anyway. Putting up 6 sacks is not a huge impact. He had literally a quarter of the pressures Kansas City's Tamba Hali had. Pressure is the real name of the game. It forces early throws, disrupts plays, and makes quarterbacks feel uncomfortable.
Saying an outside linebacker does everything well but rush the passer is in many ways like saying a car has a great paint job and sound system but just cannot transport people anywhere because it has no engine. The other stuff is nice, but the essential part is missing.