Does Hinduism have a notion of proportionate punishment?
Yes, some crimes are greater than other crimes. Also, crimes done intentionally are more punishable than crimes done unintentionally. The punishment for a crime is based on circumstances.
From the same Manusmriti:
7.16 - To men who act unlawfully, he shall mete it out appropriately, having carefully considered the time and place, as also the strength
and learning.
And from other scriptures:
Yājñavalkya (1.367).—‘The king shall inflict punishment upon those who
deserve it, after duly taking into consideration, the crime, the place
and the time, as also the strength, age, act and wealth of the
culprit,’
Gautama (12.51).—‘The award of punishment should be regulated by a
consideration of the status of the criminal, of his bodily strength,
of the nature of the crime and whether the offence has been repeated.’
Vaśiṣṭha (19, 9-10).—‘Punishment should be awarded in cases of assault
and abuse after due consideration of the particular place and time, of
the duties, age, learning, and the sect; in accordance with the
scriptures and in accordance with precedents.’
Viṣṇu (3.91, 92).—‘He should inflict punishments, corresponding to the
nature of their offences, upon evil-doers. He should inflict
punishments according to justice.’
Matsya-purāṇa (Vīramitrodaya-Rājanīti, p. 255).—‘The king should
inflict punishment after due enquiry; everything rests upon
punishment.’
Arthaśāstra (p. 32).—‘Punishment is the means whereby the security of
the science of philosophy, Vedic triad and Trade-Agriculture is
obtained.’
Śukranīti 1.45-47).—‘Through fear of punishment meted out by the king,
each man gets into the habit of following his own Dharma. The person
who follows his own Dharma can become powerful and influential in this
world. With strict adherence to one’s own duty, there can he no
happiness. Poliowing one’s own Dharma is the highest penance.’
The same concept also applies to Prayaschitta (expiation of sins)
Manu 11.209 - For the atonement of offences for which no expiation has been prescribed, one should fix an expiation after taking into
consideration the man’s capacity and the nature of the offence.