Well, on the off-chance someone at either Gearbox or 2K reads this…
Here’s (edited only for brevity) the most recent support response:
"I’m sorry to hear that you’re having this issue with Borderlands 3! I appreciate you letting me know about it.
"Thanks to Vault Hunters like yourself, we’ve been able to collect enough info about this issue to notify the development team, and they are currently working on a fix.
"Unfortunately, we don’t have visibility on their progress here in customer support, so we don’t have a timeline for the fix to be implemented. Please follow us on [snipped] as this is where the latest info, as well as, upcoming updates and fixes, will be announced.
“Please be informed that you’ll be able to mark your items if it’s in the bank or equipped.”
Here’s a verbatim copy of my response:
"Thank you for your prompt response, and I appreciate your time.
"It would appear this issue is solely in the hands of the developers; I get that, and know that patches and SW QA can take time…though this is a clearly a bug which would have been spotted after even a few minutes of play by your QA/QC team, as it’s really obvious and ubiquitous/easy to reproduce - there’s no way around seeing it, as it occurs 100% of the time.
"This leaves me having paid about a hundred dollars to be a beta tester; even worse, with hard deadlines on content (December 5th for Bloody Harvest), that also leaves me in the position of having paid for content I can’t play, so…I’m not happy about that.
"Since the Bloody Harvest patch/update came out, I’ve now spent more time perusing (and posting questions to) official and unofficial forums alike than I have playing the game itself, which, again, is souring me on it. I’m at the point where, if I could return it for a refund, I would, as I feel like I got ripped off.
"So…much as it pains me to say it (as I’ve spent hundreds of dollars on 2K games in the past, and, for example, have nothing but good things to say about BioShock 1/2/Infinite: I’d even go so far as to say those are some of my favorite games of all time, even), unless you can offer me a refund or some other form of recompense, this is definitely the last game I’ll ever purchase new from 2K/Gearbox.
"You have my money; I got burned. These things happen (though they’re not good business).
"As I got burned, and you have no recourse to offer me, I’m going to be careful to not let it happen a second time, so…lesson learned for me, I suppose.
"Unless you can offer something positive, constructive, or some form of recourse, I guess you can close this ticket.
"Again: thank you for your candor, politeness, and prompt response time. I do appreciate it, and am not looking to give you grief.
“Very Sincerely (etc)”
More bluntly put, I’m done wasting time on this, not just because it strikes me as frankly ludicrous to pay good money for something and have to spend so much time in dealing with issues it’s having due to what I suspect is inadequate QA - also because there appears to be next to zero coordination between customer service and the developers/actual companies 
I hope this post is of service or help to someone, as I’m done.
~J
(P.S.: I confess I am still quite curious to know if there is anyone playing this on a PS4 who does not have this issue; not sure if that’s enough to bring me back to the forum, though it might, if there are posts from anyone saying they are not)