All longevity are not same. Longevity with some quality is rated high. You were using an example of Ijaz to draw a parallel here. No one would have called Ijaz very good even if he had gotten 7K runs with mid 30s batting average. 
At the same time, if he had scored 10K runs, had a career average of 44-45 and performed outstanding against the best team of his era then we would have called him a very good batsman. 
You seems to think that history is full of mediocre bowlers who have 400 wickets with sub 30 average. Let's make it half and look for 200+ wickets in the last 50 years, then you will see that list will have mostly ATGs, some greats, some very good bowlers and some good bowlers.
Now if some one is fulfilling the same cut off , with 400+ wickets and a gun performance against the best team of his era then yes, he should be called a very good bowler. Sorry, Ijaz's case is not similar by any stretch. Even if he had played for 100 tests with a batting average of mid 30s , he would have been an average batsman.
Anyway, let's agree to disagree here. If you feel that Izaj's case is parallel to Kapil and only longevity separates them then it's fine. We can have a different opinion here.
Agreed. VVS was not consistent enough to be in the same league. He was a level or two below. Some posters surely over rate him here.