"Memorial" tag is always "historic" (from wiki) — yes, but that's only because the only tag for mapping a memorial is "historic=memorial". The tag "memorial=obelisk" doesn't map anything by itself, it only specifies the type of a memorial; but "historic=memorial" still is required, otherwise the object won't be shown on maps (which is why added the present object in the first place — there wasn't anything showing on the map).

Also, I suggest that you add "name:ru=Бойцам героической рабоче-крестьянской Красной армии" (and preferably in other languages also) to the older object so that it can be identified using those maps that do not process the inscription tag (most do not).