I'm not sure, but if you search online, everywhere, Proteus is the recommended simulation tool for microcontrollers.
And using Proteus, I don't know how much better Altium could make things, ie, if it can simulate like that.
altium designer is'nt a real time simulator like proteus
it's output like other vhdl simulators is waveform.
but altium designer not comparable with proteus.
Altium designer is a high power tool for designing PCB and schematics and VHDL developing.
in VHDL world a waveform out put is enough.
You must divide your design to small parts and watch its output from waveform.it is all you need.