Your question shows a lack of understanding of precedent in common law systems and the difference between "facts" and "law" in a court case and indeed how crimes are prosecuted.
Here's the potted summary -
Within any given legal system there is a law or laws that makes certain acts or omissions a crime. For example, most (but not all) criminal offences in New South Wales, Australia are codified in the Crimes Act 1900.
Have a look at DIVISION 10 - OFFENCES IN THE NATURE OF RAPE, OFFENCES RELATING TO OTHER ACTS OF SEXUAL ASSAULT ETC. The various sections in that division define the offenses of Sexual assault (s61I), Aggravated sexual assault (s61J), Aggravated sexual assault in company (s61JA), Assault with intent to have sexual intercourse (s61K), Indecent assault (s61L), Aggravated indecent assault (s61M), Act of indecency (s61N), Aggravated act of indecency (s61O) and Attempt to commit offence under sections 61I-61O (S61P), it also abolishes the common law crimes of rape and attempted rape (s63). Each of these is a different crime with different elements carrying different punishments.
A given fact pattern may suggest that one (or more) of these offences may have been committed. Police will investigate and prepare a brief of evidence for the Director of Public Prosecutions (DPP). The DPP will consider the elements and consider which elements of which crimes they believe that they can convince a jury beyond reasonable doubt that the accused committed. For example, the offence of Sexual assault (s61I) requires the DPP to prove i) there was sexual intercourse ii) without consent and iii) the accused knew there was no consent - if they do so the defendant is liable for imprisonment of up to 15 years. To prove Aggravated sexual assault (s61J) they need to prove i) to iii) above plus iv) that there were "circumstances of aggravation" (as defined) - if so, the maximum penalty is 20 years.
Now, in a common law system, the bare statements in the Crimes Act 1900 are not the totality of the law. Courts in these systems also look to precedent - which comes in binding and persuasive types. Courts are bound to follow a precedent from higher courts in their hierarchy. Court hierarchies are complicated but if you work in the system you know how this fits together. Persuasive precedents come from courts at the same level or below in your hierarchy and from courts in other hierarchies and jurisdictions with similar laws. For example, the NSW District Court may, in the absence of a binding precedent, be asked to consider a decision from the Supreme Court of Queensland or the High Court of England etc. or, of course, to an earlier decision that the particular court itself made.
The role of common law precedent is to provide consistency on the basis that similar facts should have similar outcomes. Therefore, much of the legal argument in a case is often about distinguishing the facts in this case from the facts in the case that set the precedent - that is, the facts are not similar so different outcomes are OK.
Note that parliament can always write a new law that overturns existing precedent. Indeed, the newer the law and the less precedent there is the more litigation tends to happen under that law - that's because, in the absence of precedent, no one is entirely sure what the law actually is.
When the case comes to trial there is a trier of law and a trier of fact. The trier of law decides what the law is based on statute and precedent. The trier of fact decides what happened. Usually in a criminal trial the trier of law is the judge and the trier of fact is the jury. In a civil trial (except in the USA which still uses juries in a lot of civil cases), the judge is usually both.
The job of the trier of law is to tell the trier of fact what the law is and that if they decide the facts are one way, they must convict and if they decide they are the other way they must acquit. They then leave the jury to get on with deciding the facts. For example, one of the "circumstances of aggravation" for Aggravated sexual assault is "the alleged offender breaks and enters into any dwelling-house or other building with the intention of committing the offence or any other serious indictable offence". Assume that the prosecution alleges that the accused did break and enter but the defense maintains that they were invited into the building. The judge will instruct the jury that they are to consider the evidence and decide beyond reasonable doubt if the defendant broke and entered or not and that if they decide they did then (assuming the other elements are also proved) they must decide that the defendant is guilty of Aggravated sexual assault and if they don't that they are not guilty.
Precedent can only inform the law, not the facts. Each jury decides for itself what the facts are are and what "beyond reasonable doubt" means. Therefore, the same evidence can result in different juries making different decisions. That said, in mock trials in academic studies there is remarkable consistency in verdicts - the jury system seems to work.
Crimes are all or nothing - the defendant is guilty or not guilty - there is no "worse" in the conviction. If the jury decides beyond reasonable doubt that the facts of the case are that the defendant committed all the elements of the offence then they are guilty - if not, they're not guilty.
Where "worse" does come in is when there has been a conviction, the judge decides what the sentence should be. There is a completely different law that governs this - the Crimes (Sentencing Procedure) Act 1991 and yes, this is also subject to precedent. I won't go into details here, but a judge has wide discretion to decide what the appropriate penalty should be including aggravating and mitigating circumstances and appeals are only upheld when the sentence is manifestly unjust (either too harsh or too lenient). Its interesting to note that academic studies of sentences find that, in general, judges give harsher penalties than lay people when presented with the same facts - it is only consistently the other way when the victim is a child.