I started skimming this article after a while, because it seemed to be going into the weeds of performance comparison without ever backing up to look at what the change might be doing. Which meant that I couldn't tell if I was going to be looking at the usual random noise of performance testing or something real.
For `final`, I'd want to at least see if it changing the generated code by replacing indirect vtable calls with direct or inlined calls. It might be that the compiler is already figuring it out and the keyword isn't doing anything. It might be that the compiler is changing code, but the target address was already well-predicted and it's perturbing code layout enough that it gets slower (or faster). There could be something interesting here, but I can't tell without at least a little assembly output (or perhaps a relevant portion of some intermediate representation, not that I would know which one to look at).
If it's not changing anything, then perhaps there could be an interesting investigation into the variance of performance testing in this scenario. If it's changing something, then there could be an interesting investigation into when that makes things faster vs slower. As it is, I can't tell what I should be looking for.