No problem understanding your reply.
I'm sorry to hear about your son. Unfortunately, however, once a defendant has taken a plea and been sentenced it is almost impossible for him to overturn this conviction. That's because before a judge allows any plea to be taken, he makes a record which is designed to make that plea airtight. The judge will ask questions that makes him sure that the defendant understood all of the rights he was giving up, and that, among other things, he was not forced or threatened into taking the plea. It is only when he is confident that the defendant understands what he's doing and wants the plea that the judge allows it to happen. That record will be used against the defendant whenever he turns around later and claims he didn't know what he was doing or that the plea wasn't fair.
If he has not yet been sentenced on this matter, then he would have a better chance of getting his plea back. But judges tend to do this only under extraordinary circumstances, and "buyer's regret" isn't going to be good enough. He would have to come up with a legal reason that the judge will believe, such as the fact that his attorney never fully informed him of the consequences of the plea, (if that's true) for an example.
Otherwise, he would have 30 days after his sentence to file a notice of appeal and try to get it overturned from there.
As to the other points:
1) I understand that your son was not a major drug lord. Unfortunately, however, under our present drug laws, a drug kingpin charged with a sale can face the same charges as a person selling to support his own drug habit, or the occasional seller who makes an error in judgment.
2) Police always try to "turn" someone they arrest from drugs into cooperating and giving up other names. They promise him the moon, but in fact they have no power to decide who gets arrested and who doesn't. The prosecutor controls that and doesn't take orders from the police. Police, unfortunately, are able to lie like that. The Supreme Court has established that it's okay for them to deceive in order to get information about crime.
3) No argument here. One charge is better than two, but a felony record is a felony record.
4) No argument here either. Some people do manage to transcend felonies. I even know some who went on to become professionals. But it's a much longer and harder road to personal and/or financial success.
Understand one thing: the prosecutor dropped one charge for purposes of a disposition, meaning that if he gets his plea back, he goes back to square one. He will be facing two felonies again and will have to beat both of them to do as well as whatever his present deal is. I say that because in my experience, once you go against the prosecutor on one agreement, he is not going to give him another plea. That means he'll have to try two cases.
He may have things to work with on the case, as they did wait 3 years to come after him, and that may give his lawyer some mileage, but there are never any guarantees when it comes to trials. The only guarantee the system does give you is in a negotiated plea agreement.
I realize that very little of this is what you want to hear and I am very sorry not to have better news to give you.