Meta were executing on sudden nascent demand for a well managed microblogging platform in the wake of Twitter's buyout. A 5 month copy/paste of one of their existing platforms was absolutely "building it properly" in that context.
They could have definitely spent 12-24 months building the platform diligently from naught, but they'd have the same end product, just 12 months too late. The demand could have been satisfied by any one of several players in the industry (Tiktok, bluesky, LinkedIn, Twitter itself, Snapchat, a resurrected MySpace, etc), so rushing to gain first-mover advantage was likely the singular consideration for the project.
They could have definitely spent 12-24 months building the platform diligently from naught, but they'd have the same end product, just 12 months too late. The demand could have been satisfied by any one of several players in the industry (Tiktok, bluesky, LinkedIn, Twitter itself, Snapchat, a resurrected MySpace, etc), so rushing to gain first-mover advantage was likely the singular consideration for the project.