Falconer,
in short is the 'kiss' principle a good idea?
many would say yes of course.others would disagree.In the end one can only judge by failure rates.
Whats more reliable, a s/w, a few relays, current sensors and a probe versus a clever box some wire s/w and a probe.
Done a bit of time on buses and I have changed a few PHC's.
I'd say more PHC's than failed probes on that type.
Most probes I've changed were the result of physical damage or altitude splits (in combo pitot /static probes as used on older 737 and 767 etc.)That is anecdotal evidence, you'd need to collate quite a history to have any scienctific conclusions drawn.
I'll leave any design critique to others that are more informed of the guts of the boxes in control. Been a while since I was on type and my notes are stashed somewhere.