It's possible that Canon's ILC department may not have had access to 4k encoders o
There's zero issues with cutting IPB footage in Adobe Premiere Pro. It may have been an issue with Final Cut and Avid Media Composer back in the day. It used to be pretty difficult to edit H.264, especially with Avid. But just about any half way decent computer could handle it on Premiere by 2013.
Workflow is typically dump the 4K H.264 footage(sometimes 24 or 60 fps) onto a raid. Dump it into premiere pro and plug away. Sometimes I need to grade it in resolve to deal with mixed lighting. After rough cutting in Premiere, it goes to After Effects to combine with animated typography and any effects.
If your card is fast enough, you can edit off the card when you need an immediate turnaround. This worked even on a i5 laptop from 2014.
The 4k 4:2:0 100 Mbps h.264 and 4k 4:2:0 400 Mbps ALL-I doesn't have much that's different, little bit in motion. Though, there's a world of difference when shooting with ML RAW 1080, the color is significantly better and allows you to work with tough lighting conditions. Work flow is surprisingly smooth, send straight from the card to transcode into either H.264 or Cinema DNG if lots of color grading is needed. 128 GB of footage transcodes and transfers off the card at about twice the time of copying h.264 off.