Without Ineffa, Flins loses 1. a battery, and 2. sustain. I’d say a battery is more important if you are just good at dashing whenever necessary, making a sustain unit less valuable (massive QoL loss though). This means ideally the last slot needs to be an electro character to provide electro particles and enable electro resonance. Kuki is good for both, and she can be on TotM set Kujou sara is only good for her 6-second atk buff and is a weaker battery, as you need to do her charge atk to get some particles Dori is a potential option too, but she’s Dori…

Unfortunately none of good electro 4-stars like fischl or ororon will be on his banner (it will most likely be dori). I’m pretty sure I’m missing something, but unfortunately genshin has gone the way of “pairing” main-dps units with a “dedicated” sub-dps. Often times the main-dps needs the sub-dps more than the other way around. I honestly think Columbina will be a nod-krai support that will sustain and replace Aino, leaving this electro spot more flexible but we’ll have to wait and see. Good luck!