Been using AWS Lambda for 10 years, since AWS Lambda was first released, so there really is no longer of a "time horizon" - I have not had any problems that would cause any regret, quite the opposite in fact. I also don't use the "Serverless framework", I rolled my own AWS Lambda toolchain long before the "Serverless framework" was ever a thing. So I'm not sure if the author is referring to "functions as a service" generally or specifically the "Serverless framework".
My team did recently try to set up the "Serverless framework" for a new project, and it was quickly apparent that it wasn't going to work for us. It was kind of messy, honestly. I really wanted it to work, but requiring an account on the Serverless framework website just to get Lambdas deployed was the wrong way forward for us. We just ended up using my own toolchain, which is simple and easy and does everything we need it to do, which is build the Lambda function inside AWS Lambda, and deploy the function with some basic configs.