Granted, it’s a micro benchmark without a lot of context, but wouldn’t the conclusion that the default HashMap implementation is, on average, faster than all the open addressing implementations contradict this conclusion?
Also maybe there are some tricks that can be done, to have a faster Open Addressing implementation in Java.
PS: I've also tried Cuckoo Hashing and Hopscotch and they were also slower, but haven't managed to document my findings.