CosmosDB is trustworthy? Everyone I know that used CosmosDB ended up rewriting their code because of throttling.
I know a few other teams when I was working elsewhere that had to migrate off Spanner due to throttling and random hiccups, though if Google uses it for zanzibar, they must not have that problem internally. Maybe all these companies increase throttling limits for first party use cases.
My current team uses dynamo, which has also given throttling issues, but generally only when they try to do things that it's not designed for (bulk updating a bunch of records in the same partition). Other than that, it seems reliable (incredibly consistent low latencies) and a bit cheaper than my experience with cosmos, though with fewer features.
They all seem to have their own pros and cons in my experience.