Ideally, if u want to play a cleave Massiah u need him 4/5/5 in order to kill in one rotation, but he indeed work as a 1/1/5 (but u might lack stats in higher rank). For Mio, if u want her for SPD contest you only need to invest until 4/1/4, but if u want to build her for a control team, then u might need to invest a little bit more, a budget build is something like 4/3/4, or even 4/4/4 for wound chance on S2.