Launching in a hurry to capitalize on the mistakes of your competitors is an amazing plan. Better to ship without the feature than to ship the wrong feature and be stuck with the tech debt. Better to launch and acquire users when possible, and slowly add the necessary parts.
A far more important piece than hashtags is the ability to search posts. But even that is far behind the ability to have good image sharing on posts, and Threads already does that better than Twitter, as the carousel allows far better viewing.