It's definitely a very slow database. You have to be extremely fortunate to have a problem that fits into its niche neatly. I'd sooner figure out a historical insert-only schema for PostgreSQL in future. They're not great about fixing problems with Datomic either, it feels like an afterthought. Means of overflowing labor not currently allocated to a Cognitect contract gig, not a priority in its own right.
-- sad production ex-user of Datomic