I don't think this is a significant factor in the size of the layoffs. Many high-level and high-tenure employees are being laid off, and this is apparent in many of the various companies that have had significant layoffs in the last couple years. The lay-offs have also heavily affected departments outside of engineering: product, marketing, finance, etc. have all been affected.

I don't disagree that companies greatly over-hired, but I don't think the largest portion there has been bootcamp/cert/junior SWEs.