I'm in the same boat.

If I would have to name one thing, it's that the configuration of API Gateway via the UI is unbearable if you have a nontrivial amount of routes (> 3). I need to configure Authorization, Error code mappings etc. for every route, although they are exactly the same. If there would be per-gateway defaults I can set with per-route overrides, that would cut down the setup time by 95%, which is the main thing holding me back from using API Gateway for projects that would suit it.

Right now the only option I seem to have is using a tool like Terraform to automate it, which is a pain to adopt if you already have a running API Gateway.