Well sure, we can say there's a prerequisite amount of fun to be had in the first place. Addiction is for pleasure not pain, at least for the average person. Something must not be so off-putting that you don't have a chance to get addicted. For example, a cigarette that caught your mouth on fire would probably not be smoked again. The fact that some (or even most, may be your point) games set your mouth on fire does not mean the addiction factor isn't there. It just means they're more boring than they are addictive in that critical early stage.

So we're going to no-true-scotsman our way out of this?

Nothing is binary; I'm not going to say "either leveling helps a game all the time or it doesn't". Sometimes leveling-up mechanics help a game, sometimes it doesn't, sometimes it alienates one set of users and attracts another, and there's no magic formula for when it helps and when it doesn't, and the nature of the leveling-up mechanic itself and how fun that is can vary in effectiveness dramatically. It's like having the user's avatar wear a funny hat.

I'd say that the classic "Cow Clicker" game (https://en.wikipedia.org/wiki/Cow_Clicker) is a strong counterpoint to what you're suggesting. Meant to be a satire with essentially zero gameplay, the author was surprised when it gained a dedicated following.

There is just something about the "Skinner box"-style of frequent microrewards in games that scratches an itch in the human psyche.

I think cow clicker had novelty and the empty room psych on its side as well. Humans tend to obsess upon things which seem to have a purpose but no obvious one. Nobody bats an eye at the same tree used hundreds of times of a plot important but a single beggar with grey rags instead of brown? They must be more important somehow!

Well before then players of the original Diablo were obsessively clicking cows because of rumors and belief that there had to be something to the cow.