If I would guess, for this past 3 years, CPU and software are tested and optimized on a kernel with Spectre-like mitigation-enabled. That caused a lot of trend

If I would guess, for this past 3 years, CPU and software are tested and optimized on a kernel with Spectre-like mitigation-enabled. That caused a lot of trend shifts like don't relies on automatic branch prediction, some code even explicitly avoid the speculative execution altogether, resulting no performance gain on mitigation-disabled. Even more, since they don't test on mitigation-disabled, they failed to noticed the performance issues under mitigation-disabled.