All very true, however, if you get the top specs, including a faster RAID, it can easily handle 4K from professional cameras (Alexa, EVA1, etc). I caution though that Premiere is not one of the best NLEs for editing 4K, especially when in a 1080 timeline. In my experience FCPX does a much better job. Certain format, like GH5 and some drone codecs are tougher to deal with.
The shop I work in has a mix of machines, including 5K iMacs and we deal with a lot of 4K content and cut in Premiere Pro. Because our media and projects are on a NAS, the performance is limited by the network, more so than machine power. In our case, for shorter project with faster turnarounds, we work all natively at full-res. But for longer-form projects where we have time to make a nice story, we use the Adobe proxy workflow, which is very smooth.
– Oliver
Oliver Peters – oliverpeters.com