It was conversion from standard MongoDB to RocksDB based MongoDB, so replica count calculations don't really apply.

And yes, Mongo did not optimize for space efficiency, which is why there're efforts to optimize for space efficiency.

Just like there were efforts to optimize InnoDB for space efficiency, that stalled and got derailed by these hole punching ideas.

InnoDB did not become shit, it just stalled and did not progress in an area where lots of innovation is happening elsewhere (and there were possible avenues for optimization), so it may become less relevant.

As the post [title] said, InnoDB lost its advantage.

P.S. I wrote the original post.