I may well have given your friend a different opinion.Correct you are about my home marina, channel and where I am day sailing. The channel is heavily traveled and like you mentioned well marked.
On the other hand i have a good friend that can only leave and return on high tide.
You had stated your boat, draft and sailing area - my opinion was directed only at your and your circumstances.
I run a depth finder in my boat as well as carrying a lead line. But my boat has 6 feet of draft and I'm further north on the Chesapeake than you are. I am not opposed to using different equipment - I just feel there has to be a need.
dj