Honestly I don't know why they would nerf the rewards, I see it as a slap on the face to the ones that actually need the shrines(like myself).
As Jesus said; we on s1 do need more shrines to max out runes. Only thing that comes to mind is (this is me digging deep) they are removing them from boss battle to add them for the contest like the one we just had about collecting 400 fossils and receive 15 shrines. Maybe that's intended? Idk but I still would like anything on why the nerf.