Latency on cloud run is not an issue, in my experience (been using it around 4 years now, on a fairly large scale).
Its generally fast as is, and if you want to pre-allocate a minimum # of instances, cold starts are less of a problem (basically only if you are suddenly stampeded by a spike in traffic). But the whole smart routing and localized storage concepts are left for you to implement. You can have a bunch of cloud run services behind an ELB that does geo-proximity based routing but firestore is region-bound, and cloud spanner can be very expensive. Not saying there are no workarounds but it seems to me fly.io offers a much lower cost of entry here.
No cloud Run instance supports 1000 concurrent users and stays active for 15 min after no traffic, so only a small subset of users should ever hit a cold start.
Its generally fast as is, and if you want to pre-allocate a minimum # of instances, cold starts are less of a problem (basically only if you are suddenly stampeded by a spike in traffic). But the whole smart routing and localized storage concepts are left for you to implement. You can have a bunch of cloud run services behind an ELB that does geo-proximity based routing but firestore is region-bound, and cloud spanner can be very expensive. Not saying there are no workarounds but it seems to me fly.io offers a much lower cost of entry here.