I've been doing AWS Lambda since it started up over 10 years ago. It solves a lot of problems for me. I don't ever have to worry about load balancing or scaling. I don't have to maintain a server. When it isn't being used, I am not paying for it. I've been running a pretty sophisticated project on Lambda for years, and I pay about $0.00/month for it. Most of the ~$0.45/mo I pay to AWS is in S3.

Lambda code is extremely easy to test locally, if you write it that way. I just run the file locally and it does what it would do in the cloud, there is literally no difference. But of course, YMMV depending on how you approach it.

I created my own build tools for Lambda about a month after Lambda was introduced as a product. It's been working great ever since. The workflow is very simple. When I update a file locally, it simply updates the Lambda function almost instantly. I can then test the Lambda live in the cloud. If I want to run the function locally, I just run it and it behaves the same way it would in the cloud. There's no need to run the function in AWS, if you write the code so it can be run locally. It's really, really easy to do, but I guess some people haven't figured that out yet.

I've never liked containers. It's always been way more opaque than writing Lambdas that can run locally as well as in the cloud.