IP is P2P, but a lot of the layers built on top of it are centralized, and very vulnerable to attack. DNS is hierarchical with 13 root name servers. Google is a private company, but if websearch ever goes offline, the utility of the Internet decreases dramatically. Some stupid percentage of webhosts are protected by Cloudflare; Cloudflare outages have taken large portions of the Internet offline. Same with AWS on the backend; when AWS has gone down, people find that a large number of the websites they depend upon go down too. Most people's consumer IPs are blocked off from the public Internet by their ISP and NAT.
Actually using an Internet based on IP addresses alone is ridiculously difficult. Quick, tell me how the IP protocol works using IP addresses alone! You can't type anything other than IP addresses into the address bar of your computer, and your browser can't make any secondary requests unless they're to a raw IP address. No using Google or Wikipedia unless you have their IP addresses memorized and have HOST file entries for all the secondary resources they request. You can't use HN to tell me; you need to find my computer's IP address and SSH in to me. Oh, and whatever certificate validation SSH does can't make any network requests to a DNS entry.