I’m pretty certain AI quadruples my output at least and facilitates fixing, improving and upgrading poor quality inherited software much better than in the past. Why pay for SaaS when you can build something “good enough” in a week or two? You also get exactly what you want rather than some £300k per year CRM that will double or treble in price and never quite be what you wanted.
Soon or later the CTO will be dictating which projects can be vibe coded which ones make sense to buy.
SaaS benefits from network effects - your internal tools don't. So overall SaaS is cheaper.
The reality is that software license costs is a tiny fraction of total business costs. Most of it is salaries. The situation you are describing the kind of dead spiral many companies will get into and that will be their downfall not salvation.
A lot of the SaaS target companies won't even have a CTO