It wasnt having to do with earlier models. My trezor seemed to slow down significantly after the firmware update that came right after the discovery of that attack vector. But now it's seems to be back to the way it used to be. Also I could have just been experiencing an unlucky series of server problems with mytrezor.com around that time. Not sure.
I've found that using MyTrezor with a Trezor can sometimes slow things to a complete crawl, so I don't think it's any fault of the device itself. Whenever I've had issues with my Trezor being slow with MyTrezor, I switched to using Electrum with the Trezor and it was responsive again, so I suspect that most of these slow Trezor issues lie within the MyTrezor web app.