If you could dredge out the Grand Canyon to a depth of 50km, atmospheric temperatures would be very hot – close to Venusian temperatures.
Would your hole change the height of the troposphere? Of course not. Would it change the composition of the atmosphere? Of course not. Would it change the lapse rate? Of course not.
Enough of the strawman arguments. Venus is hot because it has a thick, high pressure atmosphere. The heat has little or nothing to do with CO2. If Earth’s atmosphere were as thick as Venus, it would be incredibly hot here too.