It's not exactly like this. You don't lose the $5 difference, you lose the difference between the price that you rolled over at (In your example $35) and the price you close out later when the contract nears expiration, which should be close to the spot price. When closing out the position later, it can be at any price, can be at $20 or it can be at $35. The contango effect makes it very difficult to make money on the long side this way since you are facing a natural downward pressure for the contracts you are holding to converge downwards towards the spot price. So essentially, you buy high and settle low, rinse & repeat & you keep losing. The difference between the contract you are moving from and the one you are rolling over to is of no material importance because the price you will settle at is what matters to conclude your P/L for that cycle.
I think what he means is that once you purchase the contract, the gain or loss you experience will solely be from market fluctuations, which makes sense.
I get your point about "The futures curve remains constant", but it's the spot price which the front month price converges to at expiration (Which does not usually appear in the futures curve mostly). Even if the futures curve remains constant in spreads between expires, you buy Jun CL for $35 & Jul CL is at $40, your Jun CL will settle somewhere down near WTI spot at say $15 (By that time maybe Jul CL will be at $20 (Same $5 difference), which can settle later at any price ($10 maybe, $20, $25, you guess). Besides, the futures curve is never static, the curve is always moving & the spreads are very dynamic
If that's what he means, then I must have miss-understood it, as it was referring to the difference in price between the contracts as the loss.
I honestly have no idea what your point is. Do you dispute that contango creates unexpected losses for naive retail investors who try to buy the dip in USO? That's what this thread is about. That was a reply to me. The "he" here is referring to you. Maybe slow down and read the posts a little more carefully before replying.
This is simply not true. You buy the near month then you close out the near month. Next you purchase the far month and rinse and repeat. Pnl is realized WITHIN each contract month not across months.
If anything you should compare futures performance vs forwards, not spot. But that is besides my point. I demonstrated why your assertion is wrong in my post right before.