Yes, parental controls are not are replacement for teaching kids why this stuff is damaging. It’s not an excuse to be lazy parents. Kids need to hear their parents say it (with the why). Setting limits instead outright blocking can be helpful. It sets the stage for letting the kid decide if they would consider what they just watched be viewed as inappropriate, which believe or not does happen, but some content really shouldn’t be available to them at all.
This probably varies depending on where you live, but where I grew up (in a small town in the UK), the vast majority of 13 year olds did have access to drugs, alcohol and tobacco (which didn't necessarily mean the vast majority were indulging in those things, but they were definitely available).
I mean it’s somewhat true, if it were legal for 12 year olds to have these things AND it was marketed toward them, way more kids would be have it than not. That’s not to say they can’t get it now, but it’s harder and somewhat self regulating because the stigma around doing something illegal.
This doesn’t invalidate your point (I think your correct that making it illegal provides a disincentive and reduces overall uptake), but I should note that making something legal does not necessarily mean making it legal to market it towards kids.
Case in point being that here in the UK it is illegal to market tobacco products at all (including to adults in this case). This also applies to politicians, prescriptions medicine and a bunch of other things. And IMO it’s often a good compromise that allows for harm reduction without outright banning something.
If you want to protect your kids from these things then you need to educate them and get them to enforce the rules themselves.