One, tech isn't a massive employer. The people being employed in all the downstream businesses, the contractors, electricians, etc are in classically cyclical businesses. If this all goes south, this might not be the employment dip that starts a broad recession. Two, the debt is largely being issued by companies with some of the greatest balance sheets in the world. While the CoreWeaves etc of the world would face elimination, the classic big techs probably wouldn't. Three, it matters who the counterparty is. Right now the debt is distributed through private credit, Wall Street banks, REITs, mutual funds, etc. The contagion would reach through private credit to their LPs like pensions, insurance funds etc but as far as we know these funds are not hyper leveraged and over-indexed toward AI.
But yeah the sheer scale of the debt load just cannot be ignored.
OpenAI, Google, or SpaceX have a moat of hardware and energy. If AI is 100x cheaper orgs will use 100x more AI and the benefit of algorithmic improvements will flow to whoever has the hardware to run it.
Merely being big and doing deals is not enough for antitrust, which requires a consolidation of power and control, not merely economic decisions that could have negative side effects.
The AI industry is very big, with many actors beyond the frontier labs. There's nothing for antitrust to latch onto, except for maybe NVIDIA's deals.