I agree that there is not literally one main character. I mean more which character do you think is at the heart or core of
The Silmarillion.
For example, I think
Maedhros is perhaps the character most central to the Silmarillion's themes and story arc.
I see the Silmarillion, to some extent, as the story of the Oath of
Feanor and the ruinous consequences of pride for the
Noldor. We see Maedhros take the oath, go with the Noldor into exile, become High King briefly after Feanor's death, show nobility by relinquishing kingship to the
House of Fingolfin, display leadership and prowess in the
Wars of
Beleriand, but then ultimately descend into darkness in the Second and Third Kinslayings. Ultimately, he and
Maglor recover two of the Silmarils--only to be burned by the jewels' holy light. In despair, Maedhros casts himself into a fiery chasm, along with the Silmaril that brought so much grief for his people.
To me, Maedhros encapsulates in one character the main themes and message of the Silmarillion--of the devastating consequences of pride and rash oaths. Of the slow twisting and corruption that can happen even in pursuit of a seemingly good goal. Maedhros is around from the beginning of the story of
the Silmarils to the end. To me, his character captures the heart of the Silmarillion.