>>720461435
Ideally you want two and make them compete for first place furthering the lead from the pack. As long as one of your fronts is first on the final corner and you proc Seiun's ult you should win.
>>720460792
She's fine but he ultimate just guarantees victory IF you get to proc Seiun's ultimate, which is the front runner win state to begin with. So it's "win more" in that sense. She does get good awakening skills (concentration, left-handed) and 20% speed so she's very easy to make a good ace with.
Honestly the only annoying thing about her is how many G2's she runs in career so getting her fan count up for unique skill levels requires extra races.