Most of the software rendering list in Chromium is about more general bad behaviour, lack of features, or redundant behaviour (i.e. a GL driver is available, but it's a software renderer anyway, so might as well use Skia's software renderer), not security/full system DoS.
For example, the one at id: 3 is for renderers with the lowercase word "software" in their name; id: 1 is a GPU which does not have enough features on its mac driver to run ANGLE for GLES 2.0 (and in turn WebGL 1); id: 5 is for very old versions of mesa, where the libGL would crash (which in practice means the application would crash, but not the display/windowing servers or the display driver, nor other applications).
This behaviour on iOS is especially bad, it is not like other systems. The piece of code which would cause an issue like that is dramatically smaller on most Linux and Windows graphics stacks.
For example, the one at id: 3 is for renderers with the lowercase word "software" in their name; id: 1 is a GPU which does not have enough features on its mac driver to run ANGLE for GLES 2.0 (and in turn WebGL 1); id: 5 is for very old versions of mesa, where the libGL would crash (which in practice means the application would crash, but not the display/windowing servers or the display driver, nor other applications).
This behaviour on iOS is especially bad, it is not like other systems. The piece of code which would cause an issue like that is dramatically smaller on most Linux and Windows graphics stacks.