I think I view convenience a little different than some. We've done it both ways, and honestly, with the regular DP you still pay a good 15-20 dollars per meal in tips, and with QS your options are a bit more limited. Having to fit into a mold of what we eat is not convenient to me. I can assure you price wise, you do just fine to pay out of pocket and eat WHAT YOU WANT. We still make some table restaurant choices since we like to sit down and have our fav's. But, as other's pointed out, I may want an appetizer then, or may not want dessert, but as I'm strolling around Epcot, may want my dessert, which by the way, may cost a dollar more than a snack credit, so I'll get that item. But, if I was on the DP, I may say, Oh, that's not a snack credit, can't get it! To me, being under my own control is more convenient.
Would I accept free dining, absolutely! But we don't have that option this trip and will be paying out of pocket. Oh, and some days we just snack around grabbing whatever we want to try wherever. This food may not fit into a mold of accepted purchases. I do have 4 ADR's booked during this time of places we love, and plan on stopping by 2 that do not accept ADR's. I've done the math on everything like you did OP and I also will not be thinking with how to maximize my credits or not eat breakfast with this or that because of the credits, etc., no, our freedom = convenience to me.