The 3290 was like a 4 split tmux session, it is such a beautiful device (https://ifdesign.com/en/winner-ranking/project/ibm-3290-info...). Perfect keyboard, plasma contrast and the right text color for long sessions. My understanding is they outlived themselves with long service in air traffic control (supplementing vector/raster displays), financial markets, and software development. Once upon a time people seemed to really care about doing things well.
It does turn out that 3270 streams and web forms are similar. Transmit a form, wait for the user to fill in the fields on the form, then receive the fields when the user submits it. It is how a mainframe in the 1970s/80s can support 100s of terminals, despite being small by modern standards.
I had a PS/2 Portable 70 for a while. It was a luggable Microchannel PC with a orange plasma display. Going through airports with it was a hassle as it didn't have batteries - I would have to find an outlet to power it on for airport security inspection.
Now admittedly my own experience with the 3270 was through about three layers of obtuse IBM operating systems. Perhaps if I sat down with a 3270 and a bare OS I would consider them differently, but I always found them terribly limiting compared to a VT. More efficient sure, but much harder/impossible to do cool stuff on.
source: I was a night shift tape monkey for a IBM place for a few years. A fair amount of down time, access to a full set of manuals and an understanding boss meant I was doing more hacking on production mainframes than I probably should have been.
It was simultaneously the hardest and most pointless thing I have ever written.
Our interface to the mainframe was CMS/VSE on Z-OS. We never touched Z-OS and I was a little afraid to try, but on CMS there was REXX installed as a scripting language and I built an immediate mode character update library for it, mainly so I could sort of treat it like a VT instead of abusing the text editor(XEDIT if I remember correctly) as a ui toolkit like every other script there did, I never did figure out async keyboard reads, so probably had to poll like you said) and promptly did the first thing you do when you have access to an immediate mode text screen in the early 2000's, made a matrix screen saver. (no games because of the lack of async keyboard reads, so screen savers it was)
Anyhow the hard part, CMS REXX had no trig library, how was I going to do the hands on my analog clock without a trig library? So I smuggled in some printouts from the nist algorithm database(what an amazing website) on how to calculate sin, only to discover that REXX also had no exponent function, so the next night I smuggled in some printouts of how to calculate that. and some days later was the proud owner of an analog clock screen saver and perhaps the slowest most inefficient exponential and trig libraries to be found on CMS/REXX
I wish I could have saved the source, but... it was on a mainframe and really, I was just there to shuffle the tapes around, when my boss tried to warn me off of writing scripts I convinced him it was to help make our tape duties more productive, and for the most part it was.
I was on the DEC side with an amber VT220 and always thought it was cool that the 3270 could scream "mount me now dammit!" in flashing red block letters while the operators weren't sure if they should drop the keys or pick up the lantern.
When hired I had just missed the retirement of some sort of lockheed minicomputer they had used in the call center, which I would have loved to see. It was a very odd environment.
Years later, probably around 2003, when desktop apps started getting replaced by web apps (at least at my job), I remember making that connection between web browsers and 3270s. In the 1990s, clients got very fat (think powerbuilder), but then in the late 1990s and early 2000s much of the fat went to the server-side and the web browser became the thin(ish) client. The web browser was sort of acting as a block device (like the 3270) in the sense that the end-user filled data into fields and then sent the whole thing at once by hitting some button.
With Web 2.0, the client started to put on weight again. Then with mobile apps, the fat client was back, baby! It just keeps cycling.
I've considered the BLIT to be the platonic ideal, a seamless environment there local or remote behaved the same, looked the same and acted the same - I guess the modern equivalent to that would be Citrix applications - but thats still not as seamless.
x3270 for X11 based (it has buttons to click to send PF keys etc.)
c3270 for curses-based (terminal)
tcl3270 for using TCL to script interactions with a 3270 session
s3270 for some other form of scripting 3270 sessions
They had some hyper janky Windows XP Citrix client that ran 3270 terminals that kind of half-worked on some server somewhere, that then talked to the Big Iron. When it didn't work (it frequently didn't) it meant we got a lot of coffee breaks, so not the worst in the world.