It's funny you mention this. I'm finally getting used to the heavy mechanical engine breaking on my 2018 ATAS (manual).
I didn't like it much at first. The last time I rode a lot was in the late 70s and early 80s (my first two vehicles were used motorcycles; didn't buy a car until I was 23). If I let go of the throttle on my 1976 Kawasaki KZ650 or my 1978 Honda 750 Four K, they virtually coasted compared to this 2018 Honda.
It does certainly make the bike much safer. But it also makes it a bit clunky when shifting in the lower gears. On my bike - anyway - if you try to do a nice, slow, easy, casual take-off from stopped... you can't really do it while letting off on the throttle completely (unless you’re riding downhill). Because letting off the throttle completely brings the bike to a halt quickly (esp. in 1st, 2nd and 3rd -- but even at highway speeds and in 6th gear: I used to be able to take both hands off the bars for whatever reason, to stretch my arms a bit, or make a quick adjustment when it was safe, etc., but with this bike, if I take my hand off the throttle at 60 Mph, it slows down so fast you'd think I was using my breaks or downshifting--it's flat out impractical (or even dangerous, depending on what's behind you) to take your hand off the throttle at highway speeds. Doing 60 Mph or better on highway? Want to take your right hand off the throttle to check your back jeans pocket for your wallet? Forget about it! Unless there is no one behind you for miles. She has a very unforgiving throttle).
But your example of coming into a corner is where the engine breaking excels. Even in the higher gears. Let off the throttle and the bike slows quickly for you, helps you navigate some of the more gnarly stuff.
The 2018 ATAS Manual has 3 EB settings. I’d like a 4th or 5th. Or more difference between 1 and 3. 3 is the “least engine breaking effect” but it still breaks fairly hard. And it breaks hard in all gears and at all speeds and RPMs.
But what you are describing *is* dangerous. The bike is supposed to mechanically break and you are *used* to it doing that (and that nonsense the Technician is spouting is BS—as I described above, my bike breaks fairly hard even over 3k rpm and even at setting 3). This is a serious safety issue. Your bike is not doing what it is configured to do. I hope they fix it for you.
In the meantime, be safe and engine break the old-fashioned way… downshift.
Good luck, Gary