It is reportedly slow as molasses.
Even Casio scientific calculators have an on-calc programming language and a spreadsheet nowadays.
I had to get a TI-84 Plus CE for a college course I took a few years back. I'm an RPN guy so it pained me, but it's a nice step up from the 1990s style TI calculators. It has a fast Z80 family processor, plenty of RAM, a decent 320x240 color display, and a built-in battery that's rechargeable by USB. Usability for everything I used it for is quite good (matrix functions and some root-finding) and almost self-explanatory.
I take it out of the drawer it's in about once a year or so and standby battery life is extremely good. It must cut off power completely in standby.
It not being changed in decades appears to imply there isn't really something families see as a problem, versus others.
Casios were leagues ahead, tho.
https://brownmath.com/ti83/diff8384.htm#Catalog
In the Stone Age of graphing calculators (80s-90s), HP was dominant in engineering disciplines (and France).
Now I think maybe you’re confusing with the TI-85 (but the TI-86 was a TI-85 replacement and handles matrices just fine and superior to the 84) - so then perhaps your teacher had a TI-83. That would be more plausible and sensible.