Why The 6.x version performance is lower than 4.x

I have a quasi-production environment originally 4.2.22, but I am considering upgrading to 6.0.6. During the performance pressure test, I found that the performance difference of the pressure test results is too large. The plug-in performance of 6.0.6 is only about half of that of 4.2, because my business scenario involves a large amount of upsert logic. So version 6.0.6 doesn’t meet my performance requirements at all, so I’m curious why the performance of the new version is worse than the old version, and I checked the results of other people’s tests on the network(The downfall of MongoDB performance), and my results are basically similar. Attached is the test data of my local virtual machine for reference. Please kindly help to check whether the test conclusion is the expectation of MongoDB’s current design.