ولقد يكون به الزمان بخيلا
And time may indeed be miserly concerning him.
Yakūnu is an imperfect verb. Its temporal value cannot be moved to a past occurrence without justification. The disagreement examines whether an interpretation improperly relocates events between past and future for the sake of making the verse work.
The point is not that the imperfect always means only the future; rather, its contextual temporal force should not be ignored or rewritten without support from the expression.