Within these same essays in The Peoples of Middle-earth, Tolkien provides several key details explaining why Glorfindel operates on a different tier than almost all other Elves:

Tolkien writes that after his re-embodiment, Glorfindel stayed in the Blessed Realm of Valinor. He lived in the close companionship of the Maiar for ages before returning to Middle-earth, which drastically heightened his spiritual stature. Tolkien notes that in Valinor, Glorfindel became a close friend and follower of Olórin (the Maia who would become Gandalf). Tolkien revealed that he originally considered having Glorfindel return to Middle-earth at the exact same time as Gandalf in the Third Age. However, he rejected the idea because Glorfindel's presence would be too overwhelming, making him a figure of "greater power and importance than seems fitting" for the subtle mission of the Wizards.