If a lesser crime imposes the same or greater sentence as a more severe crime, is the punishment considered cruel?
One example, possessing a bottle of pills imposes a harsher sentence, longer term of imprisonment and exorbitant fine, than murder.
I haven't really heard of crimes having a level of 'severity' attached to them. As phoog notes, the severity of crimes are generally measured by the harshness of their sentencing. Obviously, pretending to practice witchcraft (punishable via summary conviction) would be less severe than someone such as high treason (an indictable offence where you are liable to be imprisoned for life).
The issue here is that the severity of an offence is mostly a matter of opinion, and is biased. Generally, it is the government that defines the terms for punishment. When a court strikes down a law as being "cruel or unusual", the following test is generally served well: In order for a law to be struck down, it must be "so excessive as to outrage standards of decency" or "grossly disproportionate to what would have been appropriate." In R vs Smith, a mandatory prison sentence of seven years was struck down because the law didn't consider other factors in the crime, which made it unusual punishment.
The 'severity' of the crime really depends on the case itself, and not just the name and punishment for a crime. To support this, many crimes have accompanying "circumstances", that the court must consider when trying a case. § 269.01(1) defines an example of a circumstance, aggravating circumstance - assault against a public transit operator:
Aggravating circumstance — assault against a public transit operator
269.01 (1) When a court imposes a sentence for an offence referred to in paragraph 264.1(1)(a) or any of sections 266 to 269, it shall consider as an aggravating circumstance the fact that the victim of the offence was, at the time of the commission of the offence, a public transit operator engaged in the performance of his or her duty.
It's important to note that with the myriad of cases there are, it's difficult to determine a 'severity' of an offence. While you may be able to deduce a general system to classify, it won't always be accurate. There are just too many factors to consider, and whether such a punishment would be cruel or unusual would be up to the courts to decide by individual case.
This is taken from Wex:
While the Eighth Amendment forbids grossly disproportionate punishments for capital sentences, the court is less clear on its boundaries for noncapital sentences. Capital sentences provide special constitutional protections that do not necessarily extend to noncapital sentences, as discussed in Harmelin v. Michigan, 501 U.S. 957 (1991). In Harmelin, the Justices disagreed over the existence of a proportionality requirement for noncapital sentencing proceedings. The lack of clarity on this issue was further discussed in Lockyer v. Andrade, 538 U.S. 63 (2003). In Lockyer, the Court determined that for noncapital sentences, a gross proportionality requirement is only available in “exceedingly rare” and “extreme cases.”
The Lockyer case was a guy who was sentenced to two life sentences (possibility of parole after 50 years) for stealing $150 of VHS tapes from Kmart. The procedural posture of the case is messy (finding that no federal habaes relief is available) and the facts are specific (three strikes law). But the holding is clear:
The gross disproportionality principle reserves a constitutional violation for only the extraordinary case. In applying this principle for §2254(d)(1) purposes, it was not an unreasonable application of our clearly established law for the California Court of Appeal to affirm Andrade’s sentence of two consecutive terms of 25 years to life in prison.