Those bowlers all played in a bowling friendly environment.
It's far more batsman friendly now yet bowlers still average under 25. So if anything bowlers are greater now. I just don't want to offend any past greats by degrading their abilities compared to the modern quicks. Yes maybe some of them could have still achieved attained greatness in the current era but that would be conjecture.
So you really have to factor in the rules and regulation, pitches and the type of environment bowlers have played in before making a reasonable comparison.