The CEO seems to manage the CPO & CTO relationship in these models as well, which seems like a risk given a CEO's value is investor and market / key customer facing, and any time they spend on managing the peers in the CPO/CTO relationship is opportunity cost against that value.
It also means the CPO & CTO as peers will be jockying for the CEO's attention as a deciding factor, which seems like unnecessary friction. The CPO's key relationships are to the board and supporting the CEO activities and sales key accounts with strategic feature alignment that may include M&A.
The CTO's key relationships are outward with technology partners, suppliers, vendors, etc. and downward in the org. A CTO should be a partnership with a COO role, as they are solving scale and optimization problems together.
All that is to say, depending on org maturity, I don't think CTO/CPO should be peers under the CEO. IMO one of the CPO/CTO should report to the other, as otherwise you're going to get unproductive running battles between them that cost CEO time. If you have this model and are wondering why your staff aren't working well together, it's you.
This is why it can be useful to keep a founder around as a facilitator with convening power, provided they aren't too marginalized or a loose cannon. That said, I've only consulted to orgs like this and see it across them, and this is not the view of a CEO.