It is indeed an interesting comparison. Two highly impactful players as far as Asian conditions are concerned but had issues against swing and seam and never looked half as good outside Asia as they are in the subcontinent.
However, I believe that the gap between them is clearly bigger outside Asia( YK averages 50 in England and Australia and 40+ in NZ).
Statistically, outside Asia:-
YK averages 39 against Aus, NZ, SA, WI and Eng.
Sehwag averages 35 against Aus, SA, Eng, NZ and WI.
However, things will be different if we exclude WI( YK averages 22, Sehwag averages 51) but it is a place where YK struggled heavily rather than calling it as "missing out on soft runs" as WI were minnows in the latter half of their career.
Personally, I will pick Younis beacuse although he was slightly inferior to Sehwag in Asia but clearly better than him outside Asia(stressing on their WI performance slightly only) and also had a longer career than him in a weaker side.
A lot is lost in this aggregation. Let's look at it most closely.
YK Averages Away: in AUS (1 100s): 50, Eng (2 100s): 50, NZ 43 (1 100), SL 44 (3 100) Ind 76 (3 100s) SAF 35 (1 100) WI 27 (1 100) ZIM 73 (1 100) BAN 100 (3 100)
SHW Averages Away: in AUS 46 (3 100s):
Eng: 27 (1 100) NZ 25 (0 100s)(0 100) SL 95 (3 100s) Pak 91 ( 3 100)
SAF 25 (1 100)
WI 51 ( 1 100) ZIm 51 ( 0 100) BAN 35 (0 100)
Some myths are deflated here
Sehwag was not unequivocally better than YK in Asia; he was better and more destructive than YK in SL but much worse in than YK in BAN.
At home, YK was better than SHW, average- wise, YK 59 Pak, 55 UAE, vs SHW Ind 54, though SHW was more destructive. Both were destructive when playing against their fiercest rival, Pak/Ind.
But more importantly, not only was YK much better than Sehwag in ENG, NZ, and SAF; in ENG and NZ
Sehwag did not even merit selection; (in SAF at least he scored one splendid century, but was in this sense no better than Azhar Mahmoud.)
No selector with any smarts would have picked Sehwag to open in these countries, regardless of whether the middle order is an ATG lineup of Sachins and Dravids. Not only does he
not make an World ATG XI lineup for SAF, ENG, and NZ, (and BAN) he would struggle to fit into the 10th best such lineup for these countries.
One then has to ask; yes, he would be selected for Tests in India, Pak, SL, perhaps also AUS. But if the task at hand is to open in Asia, there are plenty of players who can do a very good job. A player has lowly as Hafeez averaged 52 in the UAE, with plenty of fast daddy centuries to his credit. Would one really pick Sehwag for that possible extra oomph up front, rather than have YK in the 4th innings on a wearing pitch? Which moments are likely to be more decisive, in these conditions?
YK was a far less limited player than Sehwag in ways that have not been acknowledged on this thread. He scored a 100 in every country he played in, including WI, where he otherwise performed relatively poorly. He may not have been a first choice for a World's XI, but he would be in the second XI selected. And, going to the question at hand:
in all of these countries: SAF, ENG, NZ, BAN, ie half the world, YK, was a far far better batsman than Sehwag.
As importantly, in terms of actual performances over time, Sehwag's era of dominance was much more short lived than YK, as one would expect of someone who relied on hand eye coordination (though he was also a thinking cricketer no doubt). Sehwag was a shadow of himself in his last years, when he retired it had been 3 years since his last overseas century, and that came in SL. While continuing to pile no runs at home for some time, during those years he averaged 31, 29 and 9 at home and away combined.
By comparison YK played some of his most memorable knocks in his last years, including a memorable chase in SL, a century in Aus and a series levelling 200 in his last tour in Eng. In his last three years he averaged 66, 37 and 44. So the stats actually underplay how vast was the difference between the players as they became older:
In the last 5 years of their careers.
Sehwag, Ave away 38, 3 100s; Ave home 48, 7 100s
YK Ave away: 51, 7 100s Ave home/neutral 62 7 100s
So yes, Sehwag when on a song, during a limited period of his career, was a more destructive batsman, in certain countries, and could take games away from the opposition, in certain countries, but without taking anythig away from him, or accusing him of being a flat track bully, he is in retrospect remembered a tad too glowing for his impact; for the same reason as Afridi and Akthar were overvalued, in the former case dramatically so. (This is not to compare them, as players) They played cricket with a bang, but also went bust plenty of times.
Yet in Tests, quickness of scoring is not always the most important matter. YK too took the match away from the opposition plenty of times, in several memorable moments. And when at his best, did so more prolifically and consistently than Sehwag. Across his career, YK had a 28% likelihood of scoring a century during a match, one of the highest in history, compared for instance to 25% for Sachin, and 22 for Sehwag. YK's highest average for any calendar year is 85, Sehwag's 70.
In addition to that, YK could be counted on to score in a range of different countries, across his entire career, in all moments of a game. We know of his 4th innings exploits; he has the highest 4th innings average in the modern era of cricket, having scored 12 centuries in the second innings.
Sehwag scored only one second innings century in his entire career. Which makes it not so much a question of whether a player is able to score
"under pressure" to me - but a matter of downright liability.
And then to the most telling stat. Both batsmen were at one point in their career ranked No 1 by the ICC. But Sehwag's highest rating is 774, Younis' was 880.
Sehwag in his pomp may have awed us like few others, but there is no question that across their careers, YK was the better Test batsmen, overall.