Finding all the intricacies and gotchya's of a new framework does not happen in a couple of weeks. Also, a total workflow change is not adapted to in a couple of weeks.
That's sort of the beauty of Svelte. The surface area is minimal, and as such - though there are gotchas, you can almost count them on one hand.
I learned to use Svelte (granted, v1), in 45 minutes, and build something using it. I guarantee that a developer won't need 2 weeks to become comfortable in it.
Training doesn't happen in a vacuum. Intricacies and gotchas should be known and hopefully documented by the existing team which can help ramp a new developer up quickly
That's how you know you picked the wrong framework.