I worked in a company that used elastic search as main db. It worked, company made alot of money from that project. It was a wrong decision but helped us complete the project very fast. We needed search capability and a db. ES did it both.

Problems that we faced by using elastic search: High load, high Ram usage : db goes down, more ram needed. Luckily we had ES experts in infra team, helped us alot.(ecommerce company)

To Write and read after, you need to refresh the index or wait a refresh. More inserts, more index refreshes. Which ES is not designed for, inserts become slow. You need to find a way to insert in bulk.

Api starts, cannot find es alias because of connection issue, creates a new alias(our code did that when it cant find alias, bad idea). Oops whole data on alias is gone.

Most important thing to use ES as main db is to use "keyword" type for every field that you don't text search.

No transaction: if second insert fails you need to delete first insert by hand. Makes code look ugly.

Advantages: you can search, every field is indexed, super fast reads. Fast development. Easy to learn. We never faced data loss, even if db crashed.