The gradient of improvement is absolutely not the same.
If anything its slightly higher. Feel free to provide any evidence to the contrary.
ECI (good aggregate measure using IRT): https://epoch.ai/eci?view=graph&tab=release-date&subset-view...
METR time horizon (now topped out): https://metr.org/time-horizons/
I like this one, although its data seem to overlap with ECI.