I see your point and I'm not going to argue it. I think it's a valid one, however, I see it a bit differently because test/suites registration is not automatic in case of Boost.LT and or C++, which IMHO, is one of the main functionalities of a testing framework (it allows not to write the boilerplate code, filter, print run tests, report them, etc. which is not provided by Boost.LT out of the box).
In principle, the baseline for benchmarks could be raw functions and asserts or to compare apples to apples one could take expect from ut, BOOST_TEST from Boost.Test, CHECK from Catch2, etc. and do the manual registration as you presented, which would be fine, but not ideal, IMHO. Hence, I took the other approach and only compare frameworks that provide at least assertions/tests and suites in an automated way.
All in all, I just didn't see much value in comparing Boost.LT (not an official boost library) because, in my view, it doesn't provide the same functionality as other tested frameworks but I also see your point, is just not what I wanted to focus on in the provided benchmarks.