g. RPM dependencies are calculated from files and SONAMEs, but can also be specified manually by the packager, including version inequalities of other packages.
Debian has this too, and I think it is actually a good deal more flexible than rpm, at least from what I remember from my brief stint with Red Hat back in the day. There's a reason Debian was able to have apt long before Red Hat/Fedora had yum.
Well, then that's really a problem with the community not enforcing proper requirement standards that reflect reality on important packages.
This is the real problem. And I dare say it is 99% an Ubuntu problem because they really like to break everything with each subsequent release. Debian has been a rolling release distribution since forever and is renown for the incredible robustness with which packages can be shared between stable, testing, and even unstable, as well as the ease of transitioning from one to the other (ex: when testing becomes the new stable). And they have once or twice had to do some massive renaming of library dependencies, but managed without a hiccup, which is a testament to the quality of the deb system.
No, the problem is Ubuntu. Their versioning is a constant clusterfsck of broken, incompatible package naming. And they heavily abuse "virtual" packages for their own purposes which leads to the breakage in Samba like the GP described. It is horrible release management and is one of the many things wrong with Ubuntu. However, Ubuntu manages to stay more up-to-date, and has some pretty nifty userland tools, so I find myself using it much more than Debian. But I lament every time I have to upgrade, or if I want to move packages between versions.
Snap sounds like a system with some much-needed features, but what I would really like is for those features to be integrated into deb. Unfortunately, Ubuntu is following their usual pattern of aloofness. Both Debian and Ubuntu would benefit tremendously if they could work together to enhance deb. Transactional updates? Who doesn't want that? That is a great feature. But nope, that's not going to happen, apparently. We're going to end up with another Mir, or Upstart, or Compiz (shudder).