Long sentences are far less effective than reliable enforcement. Something that seems to be very true in practice. If you steal or vandalise something in China, there is an extremely high chance you will get caught, you won't get a massive penalty, but it will be enough to cover the damages + some.
If you for example knew that stealing had a penalty of 100% of the item value + 10% fine, with a 100% chance of getting caught, you'd never steal anything again even though the penalty is so much smaller than what it is currently in most countries. And then if you make a dumb decision as a teenager or in a lapse of judgement, it won't ruin your life.
How does that work when you don't have enough assets to cover the cost of the thing you broke or stole?
Long sentences and reliable enforcement are complimentary.
If you can reliably prosecute the repeat offenders you catch, and put them behind bars for a long time? You stop them from committing more crimes. The crime rate falls, and the amount of enforcement manpower you have available per crime rises. Making it easier to catch and prosecute the remaining offenders.
Most of the low level crime isn't done by "a dumb decision as a teenager or in a lapse of judgement". It's done by someone who has done it 5 times before and will do it again. Unless jailed, that is. The jail doesn't fix whatever's wrong with them, but it is hard to keep doing crimes while behind bars.