Ninjastic tool may not be really useful in this case because I don't see there's an option to exclude the replies and only include.thr first post of a thread means it gave thousands of mentioned replies under one board alone.
The Ninjastic tool can be useful for other things - but you're right, not in this case. You can only find out how many posts you've made on a particular board or topic - but not how many topics you've created. I try to give an example below by filling in 2 parameters:
Author: Little Mouse
Board: Services
https://ninjastic.space/search?author=Little%20Mouse&board=52