a) what ranking system are you referring to? and
b) even if we use your ranking, that means there are still 23 cornerbacks better than Porter, so to me that's not "very good," and
c) his tackling has improved dramatically? Any improvement from his first couple of years would be dramatic, so you could be right.
Joey Porter had the most pass interference penalties in the league last year with 12. Only 2 other guys had more than 9. He also had 7 defensive holding calls, while entire teams averaged less than 6. This year, he's had 8 more penalties despite missing 3.5 games, including 2 yesterday on third downs which gave Baltimore 1st-and-10s. Sauce Gardner is a physical corner too; yet somehow he hasn't had a holding or PI called since September.
Bottom line is that Porter is in year three of his pro career, hasn't changed any of his bad habits, and has gotten only marginally better while playing on one of the worst pass defense units in the NFL. Nothing emotional about it.