Aeine's theory is 100% correct. When playing for Maximum LTC, Titania just does not save any turns past Chapter 11, therefore, using her will actually "rob" other units of Cexp. She gets a tiny fraction of the Cexp that Oscar and Kieran get and she simply cannot rescue drop Mordy like they can. Lets look at each Chapter past 11.
12- Super Marcia flys out to the boss. Tits not necessary.
13- Defend map. can be done early in 7 turns. Tits not necessary.
14- Marcia go! Tits not necessary.
15- See above
16- Marcia takes Ike to the throne. Tits is only needed to get the full guard. No combat needed. Just her rescue, canto, and movement.
17- Lots of Marcia shove chains. Oscar and Kieran can rescue Mordy, Tits cant.
18- Hello Tanith, Stoned Reyson escorted by Marcia, Oscar, Kieran, and Tanith charge. Tits is the "odd man out"
19- Super Marcia 1 turn clear. Tits not necessary.
20- Siege tome the boss, Marcia arrives. Tits not necessary.
Shall I go on? When is Titania necessary for LTC past 11???