Depends how you define “profit”. If you define “profit” as the result of “exploitation”, your best argument is a tautology. You’ve cornered yourself into accepting a foregone conclusion.
I argue that profit is simply a net benefit accruing to productive activity; therefore there is such a thing as non-exploitative profit.
If the worker receives the “full product” of his labor, sometimes he will find that the “full product” is not satisfactory, given his opportunity costs. If he is wise, he’ll not make that mistake again, either adjusting or perfecting his technique, or performing a different sort of labor in the future. Other times, he will find that the “full product” was more than he had anticipated, that he has gained more than he expected to gain, and is therefore able to enjoy more leisure than he otherwise would’ve.
There is nothing per se exploitative about either of these outcomes.