Absolutely correct, I addressed both points in my conclusion - it's a momentary calculation, things change rather quickly. Though stone is still the most precious resource, considering the Grain Factor.
I personally have all resources, but 2 grain plots, so I can shift around a little if push comes to shove. Currently, I'm focused on producing more stone than anything, as it pays off. But if things balance out, I can change staked cards around.
You can find more details in Beaker's Land Tool about prices as well, as well as in the "Praetoria" community. Lots of posts about Land there. Azircon does a lot of great analytical posts and such.
RE: Production Simulation and ROI at DEC with a Leased Plot in Splinterlands: Land