Whew! Lots of embedded questions, I think; see below...
(well, fats in the afternoon/ evening, yes)
As you point out, "more balanced" should indeed be a goal. We need dietary fat to maintain T levels, maintain metabolic "fat burning" effects and offer nutraceutical benefits. It's natural for the body to start adapting to its last meal (Robertson, et al Am J Clin Nutr. 2002 Mar;75(3):505-10.) If it was low in carbs, then its logical that the subsequent meal, even much later to some extent, is less "carb ready". But eating a lot of carbs on the prior evening is more detrimental in my opinion. It supresses fat oxidation ("fat burning") and increases fat storage for say eight hours throughout the night. Also, data suggest that next-morning insulin concentrations are a bit lower after a higher fat dinner, if anything - which would lessen rather than enhance "food coma" in many people. Still, everyone is different, eh?
You know, a lack of physical activity in the morning could also be the culprit. I often suggest brisk morning walks, pre-breakfast, which could be helpful to some who have tiredness issues.
This seems odd, as most research shows a direct relationship between carb intake and performance as well as reduced fatigue. Again, everyone is different, though. In fact, I think some carb restriction 90-120 minutes prior to "fat loss cardio" is helpful.
bananas are higher glycemic index, which may be the reason
This may have something to do with adaptation to prior diet habits or sleep patterns or supplementation; I can't say. Insulin secretion can be lower in the evening, which might partly explain a lack of "food coma" but muscle receptivity to dietary carbs is also poorer, making it an inopportune time to eat lots of them.
It may be worth having your fasting insulin concentrations checked by an endocrinologist, if you have concerns. They may or may not be abnormally high and I can't say if this has anything to do with what you are experiencing. I'm only offering some general information.
Good luck finding your best lifestyle approach!