When do you really not need a separate search index (like Elasticsearch)?

We're making a new service with some simple data, and users will want to search a few text fields. Right now, I think a basic LIKE query on a good database column would work fine. But the team wants to bring in Elasticsearch from the start, just in case we need fancier search stuff down the road. I kinda feel like we might be overdoing it. So, what's your rule of thumb for when you absolutely need a separate search index versus when a regular database, even with some full-text tools, is totally okay?