I wonder whether Gentoo might have an edge here (even in general beyond just jdk) since nearly everything on the system is built with the local CPU as the optim

I wonder whether Gentoo might have an edge here (even in general beyond just jdk) since nearly everything on the system is built with the local CPU as the optimisation target? It certainly reduces the need to not be 'feint of heart' to build things too as it's part of business-as-usual. Whether Gentoo itself requires one to not be feint of heart, is definitely an open question!