They optimized for different things. The instant responsiveness of the 3270 vs. the VT at Xbps for local editing was nice. You could do async updates and even async input (via polling) as well though there was this annoying thing where the input could clash with the output and you'd get this weird icon that you had to clear (my brain is iffy on the details) e.g. when you hit a PF key while the display is updating. I think there was some workaround. I wrote some games that ran on the 3279 in an async mode (using some utilities a friend of mine built for that).