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I guess what I'm trying to say is if it's a +EV bet but allowed only to take once then what's the point of EV? One bet means nothing EVwise unless proven over a large sample.
That's nonsense and I don't think you believe it.
Let's see:
You can roll a dye once for $1 but if you win you get $1 million. You would take that bet, wouldn't you? And you would take it because of its massive, positive Expected Value. You can refuse to use the term "EV" for non-recurring bets and replace it with any other term if you wish (what would it be?), but it is what it is.
Again, what did we learn from such an exercise? What could one bet teach us if we took it? Could EV really be realized with just one bet then nothing? Nope.. That's why I'm saying it's missing the whole point of what Expected Value really is. The question in your exercise should be asking if we should bet the spot everytime even if we lose, which the answer is a resounding 'yes'.
Here's an explanation about EV with a couple of good examples.
https://upswingpoker.com/expected-value-ev-poker/