The real story isn't that some enterprise mega corp is going to vibe-code their own Workday.
The real story is that SOME startups made up of one person (or small number of engineers) will do it, and create pricing pressures against Workday, or DocuSign, or other B2B SaaS.
But if you are a mega corp, spending 0.1% of your CapEx on SaaS subscriptions, do you really want to switch to products made by some no name one person startup? You might save 0.05% of your CapEx, but if something didn’t workout, your whole business will be screwed.
To your point, I think there are 3 main categories:
1. Too big to fail (SalesForce, ServiceNow, ServiceTitan, Shopify). They’re targeting megacorps’ core business operations. Switching costs are too high. They will survive,
2. B2B non-core (PagerDuty, Vanta, Monday, Atlassian). They’re going to have stiff competition and most here will fail or merge/consolidate. They have the most to lose because they’re non-core to a business’s success and pricing pressures will cause many of them will be easily vibecoded with enough time. The large TAM here will attract hundreds of competitors each.
3. Consumer SaaS (Notion, Canva, Grammarly, Dribbble). They're good as dead and can be buried.