Imran home record is suspect for me, so let's see away first.
Imran has 180 odd wickets at avg of 26-27 when playing away against non-minnows. We have Garner/Hadlee/Marshall/Holding/Roberts etc averaging 20-23 range so it's not like pacers were not able to do well away in that era.
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Bumrah already has 170 away wickets at avg of 19-20 and counting vs IK 180 odd wickets at avg 26-27.
IK had some fantactic away series during his peak, but in Bumrah's case his entire career has been a peak. We are looking at a different class of bowler when you consider outputs in absolute terms and relative to peers.
It's not even in the same ball park.
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Now let's see home for both.
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There is nothing to suggest that Bumrah is inferior to IK in Asian conditions, but he has only 47 wickets at home so far. I will give advantage to IK here for volume.
Ik had an almost unimaginable stretch at home to pick 100 wickets.
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I firmly believe that Bumrah will cause riots if you give him bottle caps with 20 tests at home. Anyway, let's see what he ends up getting at home. If he gets to near 100 test wickets at home at avg of around 20 then career comparison between Bumrah and IK becomes one sided. So all some one can wait is to Bumrah to pick 50 home wickets at avg of 23-24. I don't think I need to wait for that given how far ahead Bumrah is in away conditions. I think some fans will wait, but I rate quality over longevity as long as large enough sample size exists to judge and 47 test wickets in Asia is way more than most ATG pacers have in Asia.
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Looking at everything, right now, I will take Bumrah over IK. More skilled, better record and he will outbowl IK on most surfaces including Asia. I suspect once Bumrah crosses 250-260 wickets, most fans won't be having this debate.