That's really up to you but Celesteela won't solve your Fini problem since Fini is neutral to steel. If anything, I'd change your team to this one
https://pokepast.es/6d09387f968792a0
This team allows you to have a secondary Mega Medicham counter and a very hard counter to aforementioned swords dancers, Kartana, Garchomp and Gliscor. You know the saying 'prevention is better than a cure'? Lele replacing Landorus would be the prevention and Garchomp serves as a backup cure. Tapu Fini is basically stall's worst nemesis. It has everything a stall team hates, status prevention, defog and taunt. Without stall's precious Dugtrio, Fini can simply come in and deny your main source of damage and remove the second one. Lele prevents this from happening by removing Fini's terrain as well as hard checking all the swords dancers and z earthquake Garchomp destroys Fini after a swords dance while simultaneously pressuring Tornadus, another pokemon that shuts this team down, altho not to the same extent as Fini
252 SpA Tapu Lele Psychic vs. 0 HP / 4 SpD Kartana in Psychic Terrain: 263-309 (101.5 - 119.3%) -- guaranteed OHKO
252 SpA Tapu Lele Psychic vs. 244 HP / 244 SpD Gliscor in Psychic Terrain: 211-249 (59.9 - 70.7%) -- guaranteed 2HKO after Poison Heal
252 SpA Tapu Lele Moonblast vs. 0 HP / 4 SpD Garchomp: 356-420 (99.7 - 117.6%) -- 93.8% chance to OHKO
252 SpA Tapu Lele Psychic vs. 0 HP / 4 SpD Garchomp in Psychic Terrain: 252-297 (70.5 - 83.1%) -- guaranteed 2HKO
As long as you inflict some minor damage to the mentioned swords dancers, Lele should be more than able to destroy them in one shot
