Currently you have 171 posts, while the topics you created are only 11 topics for now, if those 11 topics are removed the remaining 160 remain and subtract your activity from a total of 126 reduce the remaining 11 = 115 activity, thus you are still in JR's position.
No. It's not possible to delete the topics and even if the 11 topics that have been made by OP are deleted, his activity won't change.
OP has been active in 9 two-week actvity periods and his actvity is now 9*14. Even if the 11 topics are deleted, his post count will be still greater than 14*number of two-week actvity periods in which he has been active and his actvity won't decrease.
And It may worth mentioning that when it comes to activity calculation, there is no difference between a reply and a topic