Momiji have comparable eHP and better offence. Only real advantage Garret have over her is cost and tri-blocking at CC level (I'll agrue than 4-blocking after AW can be too much for him)).
And Leeanne have MORE eHP raw, and EVEN MORE eHP under her skill (vs physical attacks) than both at CC level, so really, when you want to tank thing before climbing high into Awakening levels on mentioned units, you oftentime better to use her.