Idk Soul of Cinder was a dissapointing last boss to me, wouldve rather just had Gwyn back since thats... basically kinda what Soul of Cinder is? Like a ressurected zombie Gywn wouldve worked just as well.
DS3 had some great boss fights and some of the worst like the Putrid Tree boss, the Ancient Dragon, Yhorm (basically a proto version of Rykard) and the last boss in vanilla.
Nameless King, Slave Knight Gael, Sister Friede, Darkeater Midir, Twin Demons Lords, Abyss Watchers are all goated I wont argue that
Play the DLCs bro its a fukking movie