nice diagram, don't know about your conclusion.

If you use the poker room example instead of the retail outlet example, one particular output could change hands a dozen times or more in one evening, but that gets reported as just one line in the tx, not 12. That's a credible nearly 12-fold reduction under some circumstances. A retailer (or any business) could engender something similar; take customer payments over Lightning, and make payments to suppliers/contractors also using the same Lightning hub. Any efficiency's in the way those transactions get settled on-chain can be exploited.

Also, there's more work going on right now to make the fundamentals of multisig as used by Lighning even more space efficient. Seems to me like the devs know where they're going with this overall approach to scaling up.

For certain I don't think LN makes sense to use for "one off purchases" unless those are in the form of "streaming audio/video" where you are paying per second (so payment channels are not the answer to all scalability issues at least in how I have understood that they will work).