And that wouldn't happen because..
1. Lucario is faster and will get first hit
2. If Lucario used Close combat (they are same level though) then Empoleon is part steel type and would get demolished.
3. Water type attacks to Lucario only go up to the 100th percentile which means it would do a normal amount of damage, but since you are right it is the strongest water move, it would wipe down close to 3/4 of my hp if you survive an aura sphere or a close combat.
4. Ask anyone who would win level 100 lucario or level 100 empoleon 9 out of 10 people would say Lucario.