Maybe your 29 years of experience have outlasted too long? I’ve started with electronic circuits about 50 years ago, and at that time, they all ran at 5 volt, or even combined with negative voltages - think of RS-232. In the meantime, 3.3v are common, and as you should know as an expert, many CPU’s are internally operated at levels just above levels of 1.1 volts.
The Duet originates from the (then revolutionary) Arduino Due (an Italian project, I think) - that was the first Arduino with 3.3 V (and a 32-bit ARM core). With this knowledge in mind, you should’t complain, you better should wonder why there are any 5V logic levels left.
So no: we have to deal with both logical levels, the ancient 5V and the 3.3V of modern times. Feel lucky not to have experienced the -12 V of RS-232 (not to forget the additional +12V the hard drives required at that time). For God’s sake, it’s irrelevant what you would „never ever put on the market“ or not: until now, my venerable Duet 2 is the best companion of my printer I can think of.
Not to mention the fantastic community: this forum is a collection of profound knowledge and experience - paired with (very british and quite incredible) politeness and patience of the contributors. I always found a solution for all of the problems I faced, without ever having to ask a single question: I just had to search and to read a lot.
That’s what I recommend to you, too: read before you write, think before you shout. By the way: Do you have a problem with authorities? Why else do you insist on a face-to-face with „the engineer“? Sounds to me like a bad Italo-western movie plot
If you are looking for a solution, ask. This community does the best to help you with whatever technical problem you face. However, if you are looking for a shootdown: forget it! Or, to put it in @oliof’s words: „that does not make for a good Saturday afternoon experience“.