There's nothing particularly new about a 4mm bore. That was Charatan's standard, except for bents, which were 4.7mm.
There's nothing particularly magical about 4 mm. It's a choice, not an improvement. With some traditional fine cut ribbons it's a positive menace as the ribbon gets sucked into the airway and into one's mouth.
I can't speak to current factory made product as I don't buy it, but your comments about the pipe industry NEVER making changes to their drilling and construction is patently false and screams of a lack of intellectual curiosity, and perhaps honesty as well.
And by the way, anything you write in rebuttal, or write at any time in the past or future, in the whole of the known cosmos, will be proof that I am right because I say so. See? You're not the only entity that can play that game.
The one thing you have said that has truth to it is that one doesn't need to spend a lot of money to get a good smoking pipe, something that has been reinforced repeatedly in this forum, and it is something of a straw man, since the vast majority of the money spent on high end pipes relates to aesthetics, not to airway radius.
I'll leave you with this following example of your patently, or maybe patentless, false narrative about the pipe industry too lazy to consider innovation. From 1870, and only one of thousands of examples that one can find:
View attachment 99394
I'm including this not for your benefit, but for the benefit of anyone who might be buying what you're selling.