What world are you living in?
When using a European server from Europe I expect < 10ms ping. Less than 100ms for East coast server, less than 150ms for west coast ones. Only cases I'd expect more than 200ms (and not a lot more) is when hitting Australian servers.
I'm living in reality, where a globally available application needs to serve people all over the globe from Cloudflare's >300 data centers. This means a worker running in the same data center hosting your D1 databases might get ~10ms requests, but workers running on all other >300 data centers have to pay for the round trip to the primary data center whenever there is a cache miss.
The question you need to ask yourself is how come you failed to notice that. Do you have a good grasp on what you are doing?
This is already waaaaaay too much. Same datacenter I expect nano seconds round trips. Datacenter to a datacenter on the other side of the world? Maximum 300ms. It was what you expected of game servers two decades ago. I don't see what could eat more than a couple dozen ms on the server with current hardware to make a 10ms round-trip become "> 200ms" and consider this a service you'd pay for.
I read a blog post about this but can't find it now. I did find this [release note](https://developers.cloudflare.com/d1/platform/release-notes/...) though.
They describe removing _at least_ two round trips back to the DC hosting the D1 instance.
After a cursory glance at Cloudflare D1's description and service limits, I was left with the impression that the usecases are not that of a generic RDBMS. I mean, the limit for each database is 10GB, and apparently a D1 database resides in a single location. Of course this means >200ms to even hit the server when requests don't come from the same data center.
Perhaps this is one of those things where a underperforming implementation is released to minimize time-to-market, and then they work on performance. However, for a distributed service this suggests to me that this solution only works as an ad-hoc storage of complex relational data for high-read, low-write scenarios, where you have Cloudflare Workers query D1 but either aggressively cache the response or store queries in Cloudflare KV to avoid the roundtrip cost.