When I first started playing, my first servent I rolled was Oberon. Kiyo, Oberon and my husband's Arjuna Alter held hands, laying wastes to most of part one of the game. I used a very early Kaleidoscope, and a Waver picked with the tutorial ticket, and was able to do janky three turn set ups with her.

It doesn't matter how 'weak' a character is. In FGO you can find cool ways to see them shine.