I think the implicit argument here is that "capitalism" means "rule by those who own capital." Hence a lack of unemployed people, which would hurt the captains of industry, _would_ be a failure under that definition of "capitalism."
If by "capitalism" we merely mean things like a market economy with property rights, then the question would be what to call a system that has this but where workers, rather than captains of industry, have more power? Whatever we want to call _that_ system, it doesn't currently exist, and we've seen that any moves in that direction are very strongly resisted (c.f. return to office policies driven by captains of industry freaking out).
If by "capitalism" we merely mean things like a market economy with property rights, then the question would be what to call a system that has this but where workers, rather than captains of industry, have more power? Whatever we want to call _that_ system, it doesn't currently exist, and we've seen that any moves in that direction are very strongly resisted (c.f. return to office policies driven by captains of industry freaking out).