And no, Altium isn't used by the big chip vendors for complex SoC designs. Take TI, NVidia, Microsemi and NXP for example; all their reference designs are made using Orcad.
You are not right. The manufacturers which I mentioned in my post are using Altium, ofcourse I'm not saying that they are using it exclusively, but on their webpage you can find reference designs done in Altium and it is not just a "few pieces". It is a very bold statement if you are saying that "all their reference designs are made in OrCAD" .
Read more carefully: I wrote 'Complex SoC designs'. The less complex reference designs are often outsourced to contractors and it might be that the manufacturers require them to use Altium due to the presence of Altium in the mid-range market. All in all having reference designs present in Altium format doesn't really tell you that the big manufacturers are using Altium themselves.
Take this new SoC (which is in preview phase) from TI for example: https://www.ti.com/product/DRA821U. The reference design is made using Orcad / Allegro and it is only a couple of months old.
TI is a big company, with businesses across the entire globe.
It is likely that each business unit or group, which are all pretty much autonomous anyway, chooses the tools that best meet its needs, so one may choose OrCAD, another may choose higher-end Allegro, another may choose Altium, and it would not surprise me if some future designs were done in Kicad. Why is any of this controversial?
Another point: who cares what tool is used for a reference design? A customer who uses Altium isn't going to say, "Well, shit, TI used Allegro for this SoC design, I need to get Allegro too!"