Right, so the problem here, apart from people not giving a shit, is that no-one has designed a 'spirit level for soundproofing' - a tool that can be used during the job by the builder and by the supervisor to check on it. What you have is equipment that can be used after "second fix", at which point no-one wants to rip the plaster off to fix anything, so it becomes a box ticking exercise.

There are two kinds of issue: a solid transmission path that shouldn't exist ('bridge'), and a gap or void that shouldn't exist. What we need is something like a time domain reflectometer but for sound conduction, so you can detect gaps and bridges after screwing on the drywall but before skimming over it, and before the doors have been put in - ie, while there's still a massive audio path a few meters away. Ideally, even if the next panel hasn't been screwed on. If you had that, then if it detects something then all you have to do is unscrew a panel to fix it, which is something that people might actually do.

Anyone who has enough audio engineering skills, feel free to build this!

The landlord is often not the same as the developer or construction company, and sound isolation works best when built in while the building is being constructed. Attempting to retrofit later is often less than satisfactory. So it is often not the landlord's fault, it was the developer or construction company that cut corners and used the thinnest, least sound isolating materials they could to keep their costs down.

Noise from neighbors is the biggest thing that drove me to move to a single-family home.

A lot of apartment construction must be either poorly converted or poorly constructed. I've lived in multi-unit buildings in a few places and sound isolation is pretty good. In London, I met a family at the lift and the mother apologized for how loud her children had been that weekend. My bedroom was against their living room. I honestly hadn't heard a peep.

Then here in San Francisco my particular unit is next to the garbage chute and I haven't ever heard someone putting their garbage down it. My wife and I run the 3D printer through the night and our neighbor hasn't said anything yet. It's about 57 dB from 1 m away so that's why I suppose. We do rarely hear their kids when they wail, as kids do, but not otherwise.

One of the things I do when we consider a place to live in, though, is that I play music at max volume on my wife's phone and then check from various parts of the home. I also talk to yell till my wife notices on the other side of bedroom doors and so on. To be honest, many places can be built to be quite quiet. My daughter sleeps above the work / office and it's about 29 dB right now with the printer running.

Naturally if one cannot sleep at 29 dB our home wouldn't work or you'd have to turn off the printer overnight, but overall it seems fine for me.

Where I am in British Columbia, there are sound isolation requirements in the building code so the landlords can't be cheap...but it doesn't help with older or non-permitted work.

I don't know why we don't build with concrete like the rest of the world ... that should give us a higher noise isolation than wood