18F is basically Remilia V2 with some extras.
Delay, uhh...doesn't matter tbh :V
If by "extras" you mean lower speed, much lower HP, much lower SP recovery rate, much worse leveling rate, etc., then sure.
Granted, 18F is a good character, but mostly for the 1-shot group buff. Remilia should be able to consistantly outpace him in a damage race, given her equal-or-better stat growths and better leveling rate, as well as her being in your party since the very beginning.
Banana, have you actually bothered trying out these characters in these situations, or are you just making blanket statements without any backup? In many situations, if you have your tank dedicatd to switching out slot 3 with high delay nukers, and a healer spamming cures who stays in permanently in slot 4 (like Minoriko), that still leaves slot 2 unoccupied, and without anyone dedicated to switching them out. This is where Remilia shines; even ATK-based Remilia has no problem surviving in this position.