You can emulate the Tandy in a web browser, e.g. https://dosee.link/#emulator

So if you evaluate it by hardware, it's true that the phone isn't giving the same I/O capability. But the application software is there, there are far more apps for a phone and you can access the old ones in some degree too.

If you need an actually hackable PC equivalent, we have all kinds of boards and configurations, from microcontrollers to rasPi style computers through FPGA boards. Any of them are a tiny fraction of the cost of the old desktops.