One thing that, while possible, would take time and be non-trivial is their network hardware distribution. They are have more compute locations globally than Amazon, and it's not close. And one of the main focuses Cloudflare has worked hard at doing is driving down peering prices and offering IX services to get into competitive centers.

Google could replicate this, as could Amazon (that would be more my bet personally), but Cloudflare has no vendor lock allowing customers to use any infra. Google could do the same, but it would almost always have better and more robust support on GCP, and that would create a disconnect. Same for Microsoft and Azure. They're incentivized to vendor-lock you into their compute services. Cloudflare isn't.

But, there is room for multiple competitors across the space. For instance Akamai is still a dominate player in the CDN space and Fastly has been strong. Luckily there are plenty of businesses available that they all can eat. Google muscling in might hurt Cloudflare down the line, but it wouldn't necessarily reduce the staying power of Cloudflare. Again, it's hard to achieve and undo their physical network distribution.