Utter bull,
Senju DNA works as a multiplier it enhances the potency and strength of all techniques the user has. Izanagi is a prime example, for Danzo each Sharingan would "last" a period of time granting him protection from fatal or undesirable injuries, a fatal wound would use up that "charge" without the time limit ending.
Normal Uchiha Izanagi is likely useable for a very short time, likely usable as a last moment defense rather than using it as a technique during an entire battle.
Izanami is a far less potent ability compared to Izanagi. Izanami is pseudo tsukuyomi style technique which has no effect on the real world. Its not like the same events REALLY reoccur they only do so within the genjutsu. Truthfully I am super confused as to why such a "simple" genjutsu like that requires a sharingan sacrifice. It also likely doesn't benefit from Senju DNA, I mean how would you enhance it from its current state? Have no sacrifice instead lol??
Also if it was a Senju DNA only uchiha technique then how the heck does it exist? Madara and Izuna were supposedly some of the first to unlock their MS and before that I highly doubt Uchiha were running around stealing senju DNA. Nah its just a classical example of Kishimoto writing himself into a corner and deciding "F-it I'll just ignore what I've previously said".