I'm thinking for a meaningful efficiency result you'd need to look at a lift vs power relationship because at the end of the day you want the required lift for the least amount of electrical power input.
However a practical outcome probably won't keep an academic happy.
The first "paper" is quite happy to ignore how much of the electrical energy is being converted into kinetic energy and looks soley at the resultant force of that conversion and how fast that force is moving through a body of air. That assumption simplifies the calculations to how much meaningful work the propellor is doing vs the electrical power input and NOT how much actual work it's doing vs the electrical power input, and as you've stated that formula won't work for you when that force isn't going anywhere.
So for a static system you're really sort of stuck with a resultant force vs power input rather than power out vs power in.