50 high quality home wickets is enough to put him in the top 3-5.
He does not need 50 more away, he has done enough. You have to see it on relative basis and not simply make isolated tough criterion for one bowler.
What posters is hoping here, if Bumrah does that then he will be sure shot top 3 and a strong contender for 1st spot. A long way to go for that.
It's actually not that hard to see quality of pacers. Pacers pick wickets/outbowl opposition to win tests. Batsmen scores runs/outbat opposition to win ODI's/T20. If they take 5-fers in win when playing away then it's fantastic. Only top tier pacers have been able to do that against top 3-4 teams of thier era.
You can go through entire history and find that it's extremely rare for pacers to have
good performance and 5-fers away in win in matches involving top 5 teams of their era. I listed both because some time you are lone warrior and you can't win the test, but your performance can be still quickly seen by everyone. You can limit it to 200+ career test wickets as minimum cut off to ensure some longevity.
It's too much to go through all era with screenshots, so make my point,
--------------------------------------------------------------------
In 90: Top 5 teams were,
View attachment 148857
Away 5-fers in win in matches involving top 5 teams in 90s: That's the entire list, everyone else has ZERO
View attachment 148858
Some one may point out that what about away avg without looking into 5-fers in win beacuase you may be playing for a poor team.
Away Avg of pacers in matches involving top 5 sides in 90s:
View attachment 148860
Donald, Mcgrath and Ambrose appear in top 3.
Ambrose and Mcgrath stand out in 90s when you see away avg and 5-ferts in win.
---------------------------------------------------------------------
If you do the same analysis in 80s, you will see that
Marshall and Hadlee stand out in 80s.
Steyn and Mcgrath stand out in 00s.
Bumrah and Cummins stand out in current era.
In 50 years, you have 6-7 stand out pacers. You can push for a case for 5-6 more pacers who did not stand out in either avg or 5-fers in win, but list will be still a short one. You can't come up with more than 10-12 pacers.
Older eras players were not some mythical players. We have their actual performance and impact against good teams. Honestly speaking, we had just 7-9 non-minnows in the last 50 years so top 5 teams is not too strict. If you can't have much to show in away games against good teams then you get rated lower. No one gets rated high for only stepping up against minnows or bottom teams.