Dude, every battle in Final Fantasy 7 was easy when you had Final Attack- Full-Life
Ruby, for example, I pwned with W-summon-KOTR, and instantly died from Ultima retaliation, popped back up, and repeated.
No, what you're asking is a battle without Life, Phoenix, Final Attack, KOTR, or Omnislash.
To make the Sephiroth battle harder, use the weakest gear you can find and don't use the above skills. No W-anything, Master materia, or quad magic. Don't use Final limit breaks or any multi-hit attacks. No Gil Throw or 4x stuff.
Yeah... try beating Ruby without Final Attack, W-Summon, Quadra Magic, KotR, Omnislash OR 4x Cut.
Oh, and no Elixirs, since you can copy items with W-Item...