well, Fuuka or ranger in general is pretty situational, calling them useless is a bit too far though
their main use are for map with blizzard/fog gimmick, where all unit get range reduced (and attack reduced at blizzard if i remember correctly) that might be troublesome especially if you dont have feng sui user. The last time i see map with blizzard is at gold rush anniversary though, so its better to raise normal archer in the end.
The other time ranger is used is when there is a boss monster that need to be stalled with trap, like that majin fur fur true form or shuuten douji from gold rush(the only time i bring Ricola to sortie lol).

the druid is useless, dont even bother raise her. Her token might be useful when you reach eastern country story maps though, there is flying enemy that throw spear at your unit, most range unit will die instantly. so you should keep her at least untill you get another character that can summon token.

the silver bowrider is pretty worth, though you should prioritize your core unit first.