Maybe (I'm being sassy here) there are some kind of Rock Stars problems. We can see on Arca Noae's team that there are very...very...very OS/2 skilled people involved, so there may be too many opinions that want everything perfect... and perfect is the enemy of good.
There are no "rock stars" involved, and you are correct that those who are doing the job are exceptional people. The main problem is that there are not enough of them, and every one of them is overloaded. Unfortunately, one section of the installer has proven to be somewhat dangerous, as it was implemented, and it is not easy to change it to make it more difficult for a user to hurt themselves.
The truth is that 5.0 is probably going to have some rough edges, mostly when it comes to install and reading the documentation is going to be important.
I will second that statement. The rough spot is in selecting what to install, and where, Be sure to READ the documentation, and be very careful to check that your selections are correct in the summary, before you continue. We, the testers, are not sure what they are doing to it, but it should be okay, if not elegant. This whole section will probably be changed for ArcaOS 5.1.
I will reiterate that users should have a GOOD backup of everything, and it would probably be a good idea to try the new installer on a test system, or in a virtual machine, to see what the new installer does, before you try it on a live system. The installer is similar to the eCS installer (after all, how many ways are there to install OS/2?), but there are some differences, and if the user isn't paying attention, they can get themselves into trouble.
Those who are planning to install to a machine that has a "factory" windows installed (especially if it has a recovery partition), will need to do some work to adjust the windows partitions to make room for ArcaOS, and to make the partitions fit the OS/2 way of doing partitions. Do NOT attempt to do that with any windows, or *nix, tools, or you will probably make things worse, unless you are very, very, lucky. There is a tool in ArcaOS to do it, and it works. The hard part is to shrink a recovery partition that extends past the last full cylinder on a disk. The tool does not have a good way to do the smallest required adjustment, so you need to move a large bar, by the smallest possible amount. Tricky, but possible, and you may lose a little more than what is necessary. Fortunately, that doesn't seem to matter (at least on my Lenovo ThinkPads T510, and L530). A working eCS installation should be simple, but there is no migration (which never worked anyway, even if it looked like it was okay), and there are a few differences in directory layouts, which may require a bit of adjustment, after install. I would suggest adjusting to the ArcaOS layout, when necessary.
At the moment, the installer should be workable, and the final result is actually pretty spectacular, if not perfect. I am pretty sure that there will be some problems that slip past the testers, but we tried.