We had an 18' intex ultra frame 3" out of level stand for 5 years on concrete, and we took it down due to rust - it did not collapse. We have replaced it with an xtr, which is also 3" out of level, and while I have some misgivings, I also know that IF it were to collapse... we will then be moving on to a "permanent" above ground pool. So it will be a win (as long as no one gets hurt.) (yes there is an element of husband/wife disagreement going on here... with the wife pressing the safety angle but unable to argue with the fact that the old pool did stand for 5 years)
I have a theory that being unlevel on concrete may not be as big a deal as on grass, since any additional shifting is minimized... the feet of the legs stay nice and solid and maybe that is the difference?
That said - I had a grand plan in my head to build a frame, lay a tarp, and fill it with concrete so we could have a level pool in this spot but still have the option to remove it in the future, and it would have been 400-500 dollars to pull this off. Compared to the price of a "real" above ground pool, honestly, not that bad. In my ideal dream world, my pool would be completely level, and if you can do anything to make that happen right now, I would do so.