The general concept is to only fix serious bugs in stable releases. Increasing performance is not fixing a bug - it is a feature.
Swapping out one implementation of algorithm for another is a significant change and isn't something that should go into an LTS in my view. It would be less of an issue for users if our release cadence was more frequent - but the principal applies - stability is what an LTS is aimed at. We should be fixing significant bugs only. Arguing that slower performance is a bug is specious - it works - and performance is not something that we document and guarantee. You don't find our release notes stating performance=X for a release - because such a statement makes little sense for the vast majority of users. Tim.