I had the A7ii, and traded it in for an A7Rii. Huge improvement in pixels, and low light.
I later added the A7S, and it is sooo much better in low light, both photos and video.
You'll see from my gallery that I mostly shoot in the dark.
12MP is plenty for social media use, you just have to compose correctly, where with a very high MP camera you can shoot wide, and compose in post.
JCC