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isn`t the Leo Cannon far more advanced than the Zaku?
isn`t the cannonn a beam weapon?

What battlefield? Space or Earth? Open and clear or a battlefield with obstacles?

Actually, Char has the upperhand in a space battle full of obstacles. While the MS cannot detect anything, Char's NT edge can sense hostility in people, and help him know where they are.
Zechs is definitely more at home fighting on Earth.

Uh, but it is, and we have evidence to back ourselves up.

Know what your assertions lack? Proof. Spell it with me now: P-R-O-O-F. Proof. Find some or get lost.

Why not run scenarios using all of the aforementioned variables?

Scenario Set One: Space

Location One: Earth Orbit
Conditions: Clear

We'll give Zechs' Leo the vernier backpack for this match: he'd be positively screwed without it. Considering that there isn't a separate set of stats for the space-varient Leo, we might as well say that whatever performance boosts the backpack provides are relatively minimal. The Zaku II S-type probably has the greater mobility.

As to the subject of propellent, I'm inclined to think that the Space Leo will have a greater amount of it than the Zaku II S-type. That backpack is pretty big. However, how efficient its propellent is happens to be a mystery.

[This all is, of course, conjecture on my part.]

Now, to the battle itself.

Zechs' Beam Rifle certainly sports more firepower than Char's 120mm Machine Gun or Bazooka (let's give Char his Machine Gun for the time being), but the real question is whether or not he can hit Char. If we go solely off of the Gundam Wing series--and not the "Zechs is a Newtype" mumbo-jumbo that the manga gives us--I'm inclined to believe that Char's Newtype prowess gives him the edge.

With no significant cover, it's going to be pilot-versus-pilot and machine-versus-machine. It's hard to get the drop on your enemy when you have no place to hide.

So, here's how I see this unfolding:

1. Char swoops in and fills the poor Leo full of holes before it can score a hit on him with the Beam Rifle;

2. Zechs somehow holds Char off until the "Red Comet" expends his combat propellent, forcing him to withdraw. No clear victor, though Zechs wins by default.

Location Two: Shoal Zone
Conditions: Heavy Debris

I see much the same thing happening here, though the tactics will obviously be different. This will be much more of a run-and-gun battle, with both combatants trying to surprise the other using the larger pieces of debris as cover. Outcomes:

1. Char reads Zechs and fills him full of bullets;

2. Zechs impressively fends off Char until the latter runs out of propellent and is forced to head back.

Scenario Set Two: Terrestrial Environment [Earth]

[Coming Soon!]

what he is doing is to match them equally,　ＭＳ wise
If you were to give Zechs that, then Char get`s something also
Do you not see that?

A fight between Epyon and a Zaku is pretty ******** up to begin with

Didn't I already cover the advantages Sazabi as a mobile suit has over Epyon? They're both of similar power capability, and we'll assume similar thrust in space too. But Epyon has no guns. Sazabi has a host of them. That means Epyon is dead before it gets close.