If there was enough change of a person over several millennia that his primary language evolved, the fact that the sons and daughters of Finarfn are also children of a niece he never met should not have mattered to him. Hell, a reunion with Olwe himself should have been a matter of indifference, because they would have been radically different people. But Thingol welcomes Finrod and Galadriel and their brothers like his separation from their grandfather was a relatively recent and aberrant thing in their lives and even when his pissed at their proximity to the Kinslaying and their concealment of it, he still is open to maintaining the family ties. Those should have been part of another person.
This thought is one that is poisoned by your perspective. First I agree with you in a concrete sense, but I disagree with you in an abstract sense. If we look at this question from a different point of view, from a different culture we can understand the elves, but if we use the framework of our life experiences the elves look so alien to us as humans in our current society.
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In our culture we live in today, with how the decisions, the way we survive and thrive, yes blood kin that is more than 2 generations removed to us is "noise" and we wonder why we should feel a special bond with them when we never knew them, our parents generation never knew them, but maybe our grandparents, or great grandparents knew them? Why should we care? There is an ocean of differences between us even if we share something like 1/64 to 1/4 the same blood.
But elves are immortal so how they perceive reality will be different than humans, like us elves are literally shaped by the choices they make. Immortal Elves will never perceive loss in many forms that humans must perceive loss daily.
Elves do not age, nor do they die from disease. So as long as they eat, (and not kill each other,) there is no opportunity cost for living and failing to achieve your expectations and hope. You have all the time in the world you think when you are an immortal elf like this. You have the "freedom" to obtain your goals in some future. This is so foreign to mortal men that we see elves as alien. We wish for this, but if we were given this as a gift how we perceive reality will fundamentally shift within months or years of being given this gift. We would realize the freedom that immortality gives us for some choices we have to make daily will no longer have to be made, there is no opportunity cost for many things when you can just wait.
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To understand elves we need to look at other human cultures that we will now in modern America or modern Europe will see as "alien." (Even though they are humans and not truly perfectly alien.) For example Desert Nomadic culture has a similar relationship with foreign blood ties (2 or 3 generations removed) where it is like discovering a long lost treasure. Now the nomadic cultures incentive structures and opportunity costs are completely different from immortal elves. To the immortal elves these blood kin are so long ago are possible relationships that are stuck in seed form, and we need to nurture them and they will grow into saplings and trees, and they do not feel loss like humans do for they have all the time in the world and things can evolve on their own time. Yet they treasure relationships with family they never new for they have all the time in the world. They will keep their strong memories and only develop more and more strong memories on top of them as long as the world is good, just, and there is no / little death.
Nomadic cultures treasure these blood kin from several generations ago, for so much about life is about "discovery" to them and finding things and maximizing them when they occur. Food, water, new people, etc are holy / sacred / a blessing / a generous gift from heaven, etc. It is all about discovery, and discovery determines who lives who dies, whether you have pleasure, neutrality, or pain it is the discovery that saves us or condemns the nomadic people.
Nomadic cultures can't "invest" with trying to grow food, or invest your capital into a business like we can do in modern America and Europe since the 1700s and so on. So while the immortal elves and the nomadic cultures have fundamentally different reasons they treasure kin, they actually have lots in common for the result is the same even if the incentive structure that causes it is based off different principles.
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Tolkein understood this, and he understood this is not about the concrete reality he lived in but it is a cultural thing / religious thing that is beyond space and time. It is so important to his identity for he is a "good Catholic" boy and words like satisfaction and its half a dozen meanings is such an important part of his ego / identity and how he views the world through his point of view. Satisfaction in catholic thought is not just about "Gratification" but it is also about make restitution / mending what has been broken / building for the future / paying back what was taken / atonement / vindication / and a whole lot of other meanings. (Drops the conversation about Satisfaction for I have a feeling you know what I am referring to and probably can teach me some things I do not already know, aka we can learn from each other, yadda, yadda, yadda.)
There is a quote from Westworld where a person asks a question "What is Real?" The other person thinks and responds "That which is Irreplaceable." Well when you are an immortal elves that will never die as long as you eat, and no one kills you, etc, etc it will fundamentally change what you treasure, what you value, how you experience reality for almost all forms of loss will be changed by this, all your relationships will be different if everyone can live forever. Well questions what is satisfaction? The meaning of what is real? / That is which irreplaceable! and other similar things are at the core of what I think JRR was trying to tell with The Silmarillion. A book JRR never meant to be published but was published in an incomplete state by his son. (I mention the last sentence for The Silmarillion probably could have been told better if given even more time, for JRR had an idea of what he wanted to say but he still hadn't figured out the best way to say it, to capture his mind, ideas, and values onto words.)
Why do we care and why do we not care? To answers these questions we have to examine not the literal question being asked, but instead look and observe at the other 100 questions we do each day of why do I care about X or why I don't care about X. To answer the riddle you do not take it literally but you look at it with a different space and time horizon.
