Just as PS:T is about unraveling your true nature, T:ToN is about unraveling yours, the castoffs and the changing gods.
Halfway through PS:T you meet Ravel, who with name apt unravels your nature. That you've simply lost your mortality, which nobody saw coming ッ. It's at this point you've got the whole mystery sorted out, and it all comes down to finding the fortress of regret. The only pieces of knowledge you attain past this point are related to your companions (such as Morte and Dak'kon having known the location of the portal all along), and the personal natures of your past incarnation (that your practical incarnation manipulated Deionarra and left her to die so she could be spy between the planes), none that are related to the overarching goal.
I don't need to go into more detail about it, as we all know how it plays out.
Halfway through T:ToN you learn that the ghastly figure in your mind's maze isn't a facet of yourself, but the changing god himself piggybacking along for the ride, and now he wants what he claims to belong to him; your body. Soon after you also learn that with the help of the pod that you've been looking to use up until this point, you're able merge all castoffs into one entity. So you hop about the planes, hounded by the changing gods henchmen as he's able to communicate with others using the datasphere in spite of being trapped in your mind's maze. At some point it's also revealed that you were created for the sole purpose of merging all castoffs.
Afterwards, when wandering around the hive in search of the mechanic that helped construct the pod, so that he may repair it, you not only learn that it can be used to sever the connection of all castoffs with the tide, ultimately destroying them all, and that 'The First' castoff is alive and she's looking to do just that. This leads to the final confrontation within the Hive's leaders chambers in a four-way battle. You and your companions, those loyal to the first castoff, the hive's forces and the sorrow.
Escaping 'The Sorrow', you hop into the pod and you unravel your mind's maze. Now you're up against the changing God, you've been walking in his footsteps the whole game, you've seen the world tear asunder because of his conflict with the first castoff, and now you relive his memories in the hours before you awake - only to learn that he's been dead all along, and the facet within your mind's maze is just an incomplete copy, as the Sorrow interrupted the transfer of his mind, but you do learn that he did all of this to bring back his loved ones, but that's been hinted at throughout the game already. There are also some big moments involving your companions at this point, just as there was in PS:T
And now you're thrust with the RPG trope of picking your ending.
Do you;
And then the inevitable cards of story as to what happens with everything afterwards.
As for a point? I honestly don't know. I suppose the recurring theme throughout the game is emotion and and 'the sins of the father' and torment and the use of technology without restriction, as all castoffs are suffering the consequences of the changing god. And then other castoffs has become just as grand-standing as the original creator, that leave behind more sins for the younger castoffs to deal with. I think there's a spot off free will and determinism in there too, as all castoffs were created for a purpose, but they break away from it or reinvent it.
With the exception of the revelations at the end, T:ToN doesn't match PS:T's ending in quality, it misses a couple of beats.
There's also a lack in important numenera. PS:T had the fist weapons that could permanently kill you, which you can use as leverage against the transcendant one, the bronze sphere. But I can't think of any items in T:ToN that had a significant lore revelation or weight to it. I suspect the merecasters alters the final interactions depending on what choices you make, I do know that had some immediate consequence, but I do not know the extent of it. I was able to convince the mechanic to assist me instead of the first castoff because I changed his past with the merecaster. It may even have been so that because I used the changing gods merecaster, I killed him. Though I'm not sure.
I also think it's much more poetic of TNO being forced to participate in the blood war in the good ending of PS:T than any of the endings in T:ToN