I consider that’s a brave thesis, considering the bug. “OTA update is not automatically installed via TWRP” is not fixed since 12.2019.
I assume that the S6 / S6 Edge does not have a high priority at /e/. Therefore updates are only done automatically by default. But real changes do not take place.
That’s a pity, because the S6 series are technically demanding (Exynos 7420 Octa-core, UFS 2.0 internal storage) and especially the S6 Edge are optically beautiful samrtphones. A change for the better can only be expected with the migration to /e/ OS 9-pie.