One of them took Burnley to 19th place out of 20 in the premier league, and the other took Leverkusen to 52 win season, 51 in a row, with both Bundesliga title and domestic cup (and finals at Europa too).
So we can say which manager is better, even if somehow Bayern wins the title this year, we can be certain that you can switch the managers and Bayern would definitely win the title, right now there is still a chance that Leverkusen could win and all of that is only because of Xabi, if Xabi was at Bayern and Vincent was at Leverkusen, we would have seen Bayern win the league before week 30, and see Leverkusen be 8th. It was a horrible fumble on Bayern's part to get him, I do not trust what they saw in him at all.
You have given a perfect comparison between the two managers based on their previous performance in their respective domestic leagues in the just concluded season, and according to this comparison, one can also conclude that Xavi Alonso has a better season than Vincent Kompany because even if it was Alonso that managed Burnley, they wouldn't have been relegated, even though the toughness of the Premier League might not allow him to win the title with a small team like Burnley.
If Bayern is given a chance to choose between Alonso and Kompany, they will prefer Alonso because he understands the Bundesliga and has led a team of average players to the title this season.
I am not condemning Kompany in any way, but the comparison is a bit improper, even though we know that Kompany was a player under Pep and could have learned a lot under him. I hope the expectation has been met by the Bayern Munich management because their fans are expecting them to win the Bundesliga title next season ahead of Leverkusen and Drtmund.