Yep. Looking into their model in detail, whilst it has all the simplifications of a typical economic model designed for tractability and algebraic solutions (two good economy, four agents, tax officials have perfect information) , it also adds plenty of unusual assumptions like agents moving round a grid to find resources. Which as others point out might tell us a lot about how AI can optimise strategy games (more precisely that AI optimises for values in a strategy game better than simply using the Saez formula or US federal tax brackets), but very little about the relationship between debt, taxes and investment.