What are you assuming the author case is? The article points out that by normal logic these companies are overvalued and so owning their stock is risky. Now that they've taken on all this debt, it's even riskier.

The words "valuation" and "overvalued" appear exactly 0 times in the post. The author didn't make the argument you're claiming.

Actually I misspoke in my original comment. NVIDIA has about $100 billion/year of free cash flow. So $25 billion is a quarter's free cash flow, not a half a year's.

$25 billion of debt against a $5+ trillion equity value and ~$100 billion of annual free cash flow barely moves the needle on equity beta or default risk.