copied from GSMARENA: "The Snapdragon 888 inside the Galaxy S21 Ultra maintains a higher and more stable sustained CPU performance under prolonged synthetic max load by the CPU Throttling test, compared to the Exynos 2100 model."
Please keep in mind the mentioned information only valid for controlled condition, it may not represent the real data in daily usage.
A more important aspect when analyzing today's test is the amount of performance the Exynos loses over time, compared to the much better-sustained curve on the Snapdragon. Qualcomm's chip even started to settle in and regain some ground for the final run.