The rules say that if your opponent misses your defense is wasted. This doesn’t make sense to me. You should still get the stunts for your successes, you just don’t need to reduce the damage.

That's wrong. I don't know what the translator mean with this. I'm guessing that this might be a left-over from earlier editions or something. In the Swedish edition, the sentence ends right after that you must declare that you are defending before the attacker rolls his dice. So skip the sentence "If he misses anyway, your defense is wasted".

And would it be easier for a Fight roll to be an opposed roll? And if the defender wants they can spend an action to access the effects if they beat the attacker (otherwise the attacker just misses)?

If you let melee be an opposed rolls then you will have a twice as many dice rolls during a melee round and melee would be twice as powerful compared to ranged combat. A melee expert like the warrior (Genlab Alpha) or the enforcers (who usually is a melee expert) would be extremely powerful (i.e. if they ever come into melee, your dead).

Lets do a combat example

Enforcer
Str 5
Agility 2
Fight 3
Knife 1

Chronicler
Str 3
Agility 3
Fight 1
Knife 1

Pre-round
Both roll a 4 on the Initiative roll. The Chronicler has higher Agiltiy so he goes first.

Round 1
The Chroniclers Turn:
The Chronicler attacks with 3+1+1=5 dice. The Enforcer selects defense, he will use 9 dice.
The Chronicler has 60%/81% to get a RAD. The Enforcer has 81%/95% chance to get a RAD. The Enforcer also has a much higher chance to get more than one RAD. Lets assume something on the average - the Chronicler gets 1 RAD and the Enforcer gets 2 RAD. The Enforcer use his first RAD to remove the Chroniclers RAD and he uses his second RAD to increase his Ini by 2.

The Enforcers Turn:
Nothing.
He could move or something and that can be very tactical if combined with disarm and/or tripping.

Round 2
The Enforcer (he changed his Ini last round) attacks with 9 dice and the Chronicler defend with 5 dice.
If we again uses some sort of average, we can say that this combat is over. The Enforcer could also have skipped to remove any RAD in round 1 (he can take the damage) and instead damage the Chronicler and used his second RAD to disarm. He could then move back on his turn. In round 2 in this case, the Chronicler must use a maneuver to pick up his knife but he can't attack because he is only near.

Summary:
This system clearly benefit those who uses more dice (the Enforcer if we are talking melee) and tactics. Sorry I can't see that a Chronicler is as easy to hit as an Enforcer.

But hey, the rules are easy (although they do favour tactical thinking) and easy rules can easily be changed with houserules

If the Enforcer uses Defense. If the Enforcer does not use Defense I only need one success to hit him correct? If the Chronicler does not use Defense I only need one success to hit him correct?

... and one success will give you one Stunt. The most obvious stunt, for the attacker, is of course to cause weapon damage (2 for a knife) and to increase this (one per success). The most obvious stunts, for the defender, is to eliminate attacker successes (one per success) or to counter-attack (and cause weapon damage). But there are more Stunts that can be used. It can take a while to see it but all these stunt choices actually makes the combat very tactical.

The Enforcer cannot both try to hit the Chronicler (Fight) and block the Chronicler's knife attack (Defense). He can only do one or the other. If he Fights, he leaves himself open to an attack that only needs one success to hit him if I understand the system correctly.

If we assume that the Enforcer wins the Initiative and hits the Chronicler didn't choose the defense action. He will be hit and if we assume one success he will get 2 damage. On the Chroniclers turn (he still have an action and a maneuver because he didn't use the defense action) he attacks the Enforcer. The Enforcer can choose to use the defense actions (by using his next action) or he can take his chances and hope the Chronicler misses, the Chronicler current Strength is 2 less now due to damage. So if we uses my example guys above, that would mean that the Chronicler would roll 3 dice for his attack.
If the Enforcer wins the Initiative and attacks the Chronicler and the Chronicler blocks. Then on the Chroniclers turn he will not have an action (only a maneuver). The system gives the initiative winner more freedom but the defense stunt counter-attack is dangerous.

The system works. If the Enforcer and Chronicler just hit each other back and forth (both Fight) the Enforcer will on average win with more successes with more dice. It is actually like D&D where attacks are active and AC is passive. You can parry to increase AC, it just costs you the attack. I just don't like that version of combat (because in a Fight a person would normally try for both active attack and active defense) so I'm trying to find a way around it!

No, it's not like D&D. Both side are using skill rolls and tactical option. The combat system gives you tactical choices. Normally the Initiative winner will be the attacker and by doing so forcing the other to use the defense action and thus becoming the defender. Tactical choices can change who is the attacker and who is the defender. The D&D parry option, only lets you forfeit your turn to get some extra AC. Here if you are the defender, you have a skill roll and a whole bunch of stunts to choice from. That gives you some tactical choices for you to use, trying to turn this combat into your advantage and hopefully, if your character is skilled and/or lucky, becoming the attacker yourself (or stay as a defender and be a defensive combatant). As I have said, it takes a while to get the feeling for the tactical games in melee combat.

As I mention above, if I go the Coriolis route and make Defense a Maneuver I wonder if that would work.

I don't own Coriolis so I have no idea what changes they have done and why they did it.

May I ask you if there are any difference regarding this between Coriolis and MY0?

I mean, there must be some differences if the defense is a maneuver instead of an action.