Okay. This presents something very important.
You have set down certain, specific, and most importantly limited elements that are bright-lines for you. Anything that crosses a bright line is a problem. I have no problem with that--but the key word here is limited.
The presentation, consistently--and as noted, what I just quoted from Bloodtide in a very recent post--is that the GM can create bright lines at any time, for any reason, as frequently as they like. They can add or remove bright lines whenever they want, for whatever reason they want, including for no reason at all. Any time they want a bright line, it's there. Any time they don't, it's not. A bright line might flick back and forth numerous times. Etc.
That's when it becomes a problem, where one side has arbitrary, unlimited, unchecked power to draw bright lines. Having some of them is good, possibly even great--but that "some" needs to be relatively limited, not carte blanche. Otherwise, yeah, it really does look like demanding absolute and unchecked power to be used at whatever arbitrary times the holder feels like.
You gave as an example where you intentionally don't draw any bright lines around stuff like new classes. That seems a pretty stark exception from the way "traditional GMs" present their work, where everything gets almost coated in bright lines. Sharply constrained classes, and races, and backgrounds, and concepts, and approaches, etc., etc., etc. That's where the "better toe the line" side comes from.
Also I'm not sure what "BL" means in this context. Bottom line?
Edit:
To add something that would forestall the possibility that others might read a false narrative into the above, this should apply to EVERYONE. NOBODY gets free rein to write bright lines anywhere and everywhere they like.
Because I am 100% sure someone would respond to the above with "OH SO THE GM IS JUST THE PLAYERS' SLAVE HUH!!??!!"