You didn't understand his post, if his last seen is recently, he want his sent history be hidden too and not like the way public we know about his activity. It kills the purpose of last seen been private if the user last seen is recently only for his merit sent activity to be 10 minutes ago, there is no privacy.
The same applies to posts.
What does it matter to hide when you were last online, if you have a post that was made 10 minutes ago?
This function is only viable for those who want to visit the forum just to read and not interact with it. Because if you interact, you will be exposing your presence.
By keeping hidden not only the last time someone was online, but also their most recent interactions, especially their merits, they are forcing others to keep their activities hidden as well.
In other words, if I receive a merit award, and I don't know I received it simply because someone decided to hide that they were online, they are also hiding my activity. I'm not saying this out of obsession with merit or anything like that. It's just simple logic: if my activity interferes with the activity of others, it shouldn't be hidden.
I believe the logic behind the option to hide the last time one was online is indeed to maintain privacy, but for this to be effective, the person cannot interact in the forum. Without questioning how hiding the last time someone was online guarantees privacy. But one thing is certain: for this to work without impacting others, the person cannot interact.
We have a lot to learn from Satoshi regarding privacy. He was active at a time when the notion of privacy wasn't taken so seriously. The forum didn't have these things about hiding anything. And even today, nobody knows who he is.