The area enclosed by a loop is the total work done. If you draw a square, isn't that the maximum amount of work done possible instead. Why is the isothermal/adiabatic path the most efficient instead of a simple square? It seems that an isobaric path gives the most work per area.
Best Answer
My first observation regarding your drawing of the cycle is that while you are showing heat being added during the isobaric expansion work, you do not show that heat is also being added during the isochoric pressure increase which produces no work. For the Carnot cycle all of the heat added produces work.
But more importantly, it also appears that you are comparing the work done in the isochoric-isobaric cycle with the work done in the Carnot cycle when both cycles operate over the same range of volumes, as shown in FIG 1 below. The problem with the comparison is that the isochoric-isobaric cycle is operating over a greater temperature range than the Carnot cycle. Note that in FIG 1 for the isochoric-isobaric cycle the maximum temperature is greater than that of the Carnot cycle and minimum temperature is less than the Carnot cycle. Thus in terms of thermal efficiency, it's mixing apples and oranges.
The Carnot cycle is the most efficient cycle over a given temperature range. So to compare the work and efficiency of your cycle with the Carnot cycle, you need to compare the two over the same temperature range, as shown in FIG 2 below.
Hope this helps.