Re: Partitioning
"On every laptop I've used I always had /home on a separate partition, and just NEVER have I run out of space on / or /usr due to stuff happening there."
Yes, that's probably the most normal situation. After all, you're unlikely to suddenly decide you need tens of gigabytes new software one day. However, if you ever did, the partition situation could make it hard to install that. If you kept a bunch of space around for the case where you did, then you're unnecessarily restricting the space available for /home.
In my case, on the systems where /home is sharing with /usr, I don't pretend my usage is normal. I have an old device with a 128 GB drive which is used for a bunch of random, at times experimental purposes. I decided to test out the Gitlab CE software by installing it on that (for those who haven't done this, it brings its own Nginx version, a bunch of Ruby libraries, is rather large in itself, and is designed to store data outside the home directories). When I was done experimenting with that, I removed it. Having one partition gave me the flexibility to do that without repartitioning either time. You don't have to do that, and if you don't or have a larger disk (I got the laptop for free from a user who wanted it junked), you probably won't encounter the situation very often.
That said, try explaining to a standard user why they should do that. Not with the separate disks situation, not with a server, just a standard user with a single disk that all the partitions are going to go on, a user who already backs up their data. What benefits can this provide that justifies the extra complexity, complexity that is absent on lots of other systems and optional here? The best reasons I've heard that apply here are as follows:
If /home is separate, you don't have to replace it when you reinstall. This assumes that you'll be reinstalling a lot, which they probably won't, and it also assumes that every installation will be smart enough to figure this out, not repartition, not create a new partition for /home, and correctly mount it later on (this last one is mostly an editing of fstab if it doesn't, but if you have to manually reconfigure your filesystems and don't get anything out of it, maybe not so useful). A correllary to this argument is that it's harder to trash the /home partition. The user can point out that the chances of breaking their home directory are already quite low, most likely ways will use the filesystem instead of the partition and won't care where the home directory is, and that they have backups to deal with both.
There are lots of good arguments for keeping /home on a different partition. In each case I can think of, it's a case where, if you ask "Why do you have it partitioned this way", the user will have a specific set of benefits that doing so provides them and that they know about. It's possible that there has always been a clear benefit that keeping the partitions separate provides, even when a user isn't doing it to implement a desired feature, but if there is, I do not understand it. I would welcome learning that lesson, but it should be better than "We do it this way because most Unix servers do it this way and, even though they have lots of reasons that don't apply to this, we must follow them".