Sure, increasing debt is doing just that - spending future revenues ahead of their actual arrival. Same as any credit.
Our effective working capital - from a football (not just financial) perspective - is the total value of the squad, plus cash at hand. And by running with little debt we are effectively reducing that total working capital, which means a thinner squad than our rivals.
We don't have to keep ballooning debt forever, but if we chose as a one off to shift our debt level to (say) £300m (still £200m less than Man U for example), then we'd have 2 or 3 more high class players in the squad, always. The only risks we'd bear is (1) if the market for players completely craters, making us unable to liquidate value in our squad, or (2) if we stop running the rest of our operations the way we have been for 4 or 5 years now - growing commercial revenues, selling on youth players for decent money, selling older players for top dollar etc.
The way FSG are running us right now makes perfect sense if your goal is an exit in about 3-5 years, but means you're relying on a lot of luck that your thin squad doesn't get exposed at any point by injuries, suspensions etc.
Edit: additionally, our debt-to-value ratio is absurdly lower than under H&G, before anyone starts talking about unsustainable loading of debt.