The TI 84 is like the AK47 of calculators. While it has decades old tech, good performance and an intuitive UI make it a favorite amongst industry professionals today.
Texas Instruments didn't mean to rip us off with 80s tech. They just have yet to surpass it.
But they have tried. The TI 85, for instance, is a stronger beast, but it's a lot harder to use. The TI Nspire has a ton of functionality and can even begin to rival lower end phones in sheer processing power, but its UI is abhorrent to the point of being unusable.
In terms of power, though, the TI 84 is like the Toyota AE 86. It does everything you need it to eloquently and quickly, and you can mod it to increase power at the cost of stability. I'd totally see it being Takumi's go-to calculator.
All in all, the TI 84 is the best graphing calculator on the market. The only reason not to use it is if you're in a class that requires a nonprogrammable scientific calculator. Even then, if you can get away with using the TI 84, you'll be better off.
Note: I have NO affiliations with Texas Instruments. I just think this is a great calculator, especially considering its low price tag.