To be fair, Tierney has been on the list for 2 more years than Kavanagh, and is more experienced as well, so I am not sure where this idea that he has overtaken Chris has come from. Kavanagh is 5 years younger, so I would expect him to grow even more in time - plus he has had the Manchester derby this season, so he is in a pretty good position himself.
That said, this is undoubtedly his biggest match so far, and a clear sign he is trusted with the biggest matches now. I would have him as a favourite for one of the finals this year.
Rob Jones is the only referee to not get a game across either of the midweek rounds, or the weekend round.
Unless I am mistaken, Chris is category 1 and Tierney is category 2 still. I would say on that basis, Kavanagh is ahead of Paul..