Not true, it is the Echo itself that prevents tempering not the Blessing, although the Blessing of Light is connected with the Echo, the two are different (hence why when Midgardsormr seals the Blessing the player can still go and destroy Primals without risk of tempering, the Echo is unaffected and is what grants them immunity from Primal influence).
Also even in 1.0 when the Blessing did not exist the adventurer pre-Calamity was protected from Ifrit's tempering back when Ifrit appeared for the very first time, having only the Echo to protect them.
No, it's clear it's the Echo that protects a person from Primal influence (tempering), not the Blessing of Light (the later which is the manifestation of a mandala that allows the Crystals of Light to appear and function as a direct interface with Hydaelyn Herself).
