> Sharing ideas gets people thinking and the fact that someone else already extensively thought about something doesn't make my thoughts less relevant. If anything, by sharing it I could get a comment pointing me to a book or paper that would help me understand better the topic or expand my ideas further.

"Relevant" needs disambiguation. It does not make your thoughts less valid in any moral sense that you should feel ashamed of them or anything, but IMO, it does mean that they are less worthy in the attention marketplace. If these thoughts are not competing in the attention marketplace, and rather being shared amongst acquaintances, or offered up in the aim of constructive criticism, then it does not risk turning the attention marketplace into a competition of hustling mediocrity.

> Should then all philosopher in history not write anything because it was not really an original thought?

Most (continental) philosophy is closer to art in my opinion than scientific inquiry. If you accept it as art, then you at least open the door to there being many valuably different ways of saying "love is good" or "reality is complicated" or what have you. And if you consider it as something beyond art, well, then it has some very pointed questions to answer.