I think some perspective is needed when evaluating this sort of thing. Would I use a home made 3D printed HV probe to measure the primary of a distribution pole pig or a 50kVa 150kVp xray transformer? Heck no, but for the sort of hobby HV stuff most of us are likely to encounter? Sure, why not? I played with CRT flyback transformers and neon sign transformers for many years using various scraps of plastic and strings of 1/4W resistors before I got a proper Fluke HV probe. It is seriously over-engineered for typical hobby stuff but it came in handy when I wanted to measure the output of MOTs and later the 4160V output of a pole pig we were using to power a HV series streetlighting regulator used for testing some products I was involved in. These sort of not only high voltage but high energy things is where it's worth splurging on the real deal.
Yet if someones scope is inadvertently floated due to a poor or NO mains earth there would be no protective gain.
I am a fan of redundant protective earth connections. Extra effort, but making any such measurement requires a set of precautions when setting up.