Final Cutter and Spring should both go above Fludd imo. Fludd is too slow unlike Water Gun, harder the charge up, and hardly helps out. Final cutter gives you a bit more mobility to not be punished after it and Spring can be used for edgegaurding and giving yourself a safe landing.
Fludd helps to gimp people - practically the whole cast, save a few that it actually aids in recovering like Peach and G&W.
Gimps people single handedly - Ask the Spacies, Ness, or Ike.
Creates vulnerabilities with characters that have high priority - FIHL makes matchups like Marth, G&W and Peach a little more bearable onstage with proper Fludd usage.
Helps deal with projectiles - See long list of projectiles it cancels out, and then see the items that it protects from like nades and suit pieces.
And is a good recovery tool - recovery defense, not recovery boost as you may be thinking.
Watergun also doesn't push as far as Fludd, it's just easier to charge and does damage when it's not charged. Even if I am exaggerating (which may or may not be true) Fludd DOES do all of these things
to some extent. Not to put down Final Cutter or Spring, but they have fewer uses, and aren't staples in either character's playstyle.
Edit @ <3: Sheik's needles are high enough at 15th...everything projectile above it (including the needles themselves) is fantastic, and nearly interchangeable anyway.