This is complete nonsense and probably just made up. The previous MB Pro design required adapters for the VAST majority of all monitors. There's nothing new here.
If jonjenk is doing hardware development, I can sympathize. I'll attest that literally nothing in my current bench environment is USB-C compatible. Dev boards, JTAG debuggers, emulators, UART bridges, signal scopes, SoCs...all USB 2.0.
Maybe he's talking about stuff other than charging cables and monitors?
I would be shocked if most USB accessories didn't work with an adaptor. The old macbook only had two USB A ports anyway. I do hardware development and use a USB hub with my 2015 Macbook Pro. I'm guessing USB-C to to USB-A hubs exist and work well.
Yes, ditching physical compatibility with nearly every other connector currently in use, in exchange for a millimeter or two of thinness, is the rational option.
They exist, but if you read OP's statement "Our engineers refuse to engage in the dongle shenanigans" you can also see that they just didn't want to have more hubs to juggle in the course of their day.
In my limited experience, HDMI is the new VGA in terms of availability. Projectors, TVs, screens all support it (even if it can't drive 10-bit modes or the max refresh rate).
If you bring a HDMI-capable Mac to a client and something doesn't work, it's their fault. If you bring a USB-C Mac and forget the dongle, it feels like a faux pas on your end.
Though to be fair, it was an aberration that the last (fantastic!) rMBP had a useful video port. Historically, portable Macs always needed crappy adapters.
Err I have had my 15" rMBP and have never needed a dongle. It supports thunderbolt/displayport and HDMI. I can connect not only to multiple monitors easily without dongles, I can connect to TVs.
The all USB-C design of the new Pros is not very Pro friendly. It should be the base MacBook.
Maybe he's talking about stuff other than charging cables and monitors?