Your analysis looks good, but it's a little long.

You say that once you accelerate to cruising speed, you need little effort to maintain that speed. That's true if you have perfect cadence. But if you're like me and you don't, you need greater force twice every crank revolution to accelerate your load. That adds up.

There's another factor: Whether you can actually carry the load or not. (Sorry, I didn't read every word of your long post, so forgive me if you did cover this.) Some of us, as we age or get hurt, find we can simply no longer carry what we did in our younger days, and we must greatly lighten our loads to continue just getting on the bike. This might require a large, radical shift, beyond considering the marginal "cost" of an individual item. Deciding to take the leap to carrying a tarp and a quilt and not cooking are examples. Going rackless is another. Or even switching from camping to inns.