Aside from the very valid points others have raised...
Of course you can lose some weight in the short term by gaming energy balance. And the reason said experiment has been done "again and again and time again" is because in the long term, you will need to consistently cut more and/or burn more to keep losing the same amount of weight, and in 95% or more of cases you will be unable to keep that up, and eventually will gain that weight back and likely more.
The person who suffers giganticism will also lose weight with such a strategy. But no one would suggest that restricting intake or increasing expenditure will *cure* giganticism, or that too much expenditure *caused* it...we recognize that it is a hormonal problem that cause a person to grow abnormally. Even though thermodynamics apply as surely as it does with obesity (and indeed you can stunt developmental growth through starvation), they is not the primary or even really a particularly relevant factor.
Now that doesn't mean that obesity isn't caused by simple caloric excess, but it does prove that thermodynamics do not make it necessarily so. In fact, the only way one would be justified in claiming such a thing was if you could (a) prove beyond any reasonable doubt that there is no similar biological disruption involved in common obesity, or (b) show clinical results where simply trying to create negative energy balance via caloric restriction and increased exertion (aka standard diet and exercise advice) reliably reverses obesity over the long term. There is far too much evidence otherwise to claim (a), and the only way you can justify (b) is through the the standard rationalization practiced by the medical community today..."it's not true that our standard prescription of diet/exercise is 95+% ineffective, it's 100% effective but there's a 95+% non-compliance rate." Of course it's a tautology, the only indicator of 'compliance' is success...and you easily could substitute 'prayer' for 'diet/exercise' and it would be just as true. (You didn't lose weight, obviously you're not praying hard enough, fatty!)
So does the fact that you can temporarily shed some weight by effectively starving yourself via diet or exertion justify your initial claim that simple control of caloric balance (whatever that even means in the real world) is the "precisely one thing...nothing else" that a fatty needs to know to be a former fatty? It may be the conventional wisdom, but, to use the vernacular, it's fucking retarded.