I left Sketch 18 months ago for Figma on a job switch, and I can tell you that writing plugins for Figma is an absolute joy compared to Sketch. Why? Because Figma's API documentation is complete.
Creating Figma plugins, you don't have to read the tea leaves of some header file to find out what parameters a function takes, or scour other creators' Github repos to find out how to use undocumented functions: every bit of it is there. And it's all in straight-up TypeScript.
Did you know using Sketch's plugin API that you can turn off proportion constraints before resizing a layer? You certainly wouldn't if you read every word of Sketch's API documentation. Did Sketch decide to deprecate a function, breaking your plugin? Better hit the forums, because Sketch will make no mention of it.
To be clear, I don't blame the writers. From the outside this looks like a screwed-up process flow within the company. If anyone is to blame, it's the CIO for not creating the process, and the CTO for having such a terrible plugin development environment. Hey CTO, look at Figma's API and weep.
Sketch is losing customers to Figma in a steady stream. I certainly would dread taking on a Sketch-based job again, for plug-in creation alone. This seems like an easy hole to plug.