The 7333A is a linear regulator, which means it drops voltage by converting power to heat. Typically those make sense when the input voltage is close to the output voltage or the load is very small. If it’s getting too hot, the load is high enough that the efficiency will be very bad…whether or not this is a problem depends on your application.
Some random site claims 170mA and another claims up to 400mA. 170mA * 8.7V (12V in minus 3.3V out) = about 1.5 watts, which is too much for a TO-92 package.
Can you use a tiny buck converter instead? Or a larger package for the linear regulator that can add a small heat sink?
As for your actual circuit, the second transistor is an interesting idea (you’re using it to invert the state so you can have the GPIO pulled in the non-problematic direction?) and I don’t have enough experience to give further suggestions.
I’m not entirely clear on the problem, but yes - the circuit as drawn makes the microcontroller pin start high, then fall after some time. Do you need the microcontroller pin to have a different voltage than the transistor base (I assume when you said gate you mean base…gates are for FETs), or is this good enough?
It’s similar to AC-DC. From a simplistic perspective, efficiency at idle will be 0% because the converter itself still uses some power, then efficiency increases with load since the converter overhead becomes less significant as the useful work increases. Googling “dc dc converter efficiency curve” gives plenty of results.