I think this movie has a lot similarities with the MMO SWTOR's KOTET xpc ending.
1)
The Emperor rez from dead, tried to seduce and possess the hero's body. Valkorion almost succeeded.
2)
The Throne and the fleet. Palpatine has a throne and massive fleet to conquer the galaxy. Valkorion has the Eternal Throne to conquer the galaxy.
The final duel was around the throne, about the fleet, just KOTET was using mind battle.
3)
The Emperor and his daughter/grand daughter
Palpatine was afraid of his granddaughter Rey's power, he tried to kill/use her and her parent went away to hide her. Valkorion was afraid of his daughter Vaylin's power, he used ritual and terrible torture to turn Vaylin into a monster.
Dark Rey's illusion was very similar to Vaylin in the cinematic.
Rey=KOTET PC with Vaylin's background just got lucky
4)
The betrayer and usurper.
Kylo Ren and Arcann both killed their father, both killed the Empire/FO's leader when the hero got captured. They both wear masks and were redeemed by their mother(light side). Both aided the hero in the final battle.
5)
The Emperor absorbed his daughter/granddauguther's power
Palpatine drained Rey and Kylo's power to regain his strength.
Valkorion drained Vaylin and Arcann(if not redeemed)'s soul power to fully possess the hero.
6)
Lightning blast ships
Palpatine used it. PC can chose to accept Valkorion's power and blasted many ships when fighting Arcann in KOTFE.
7)
The final death of the emperor
Palpatine got his lightning turned back and exploded. Valkorion got his dark power and lightning turned back with the saberstrike and exploded