There are other serializers like blueprinter [0]. I haven't used it yet, but it seems like a good (fast) AMS replacement.
I also recommend using Oj [1] which is a very fast JSON parser/generator for Ruby.
JSON generating through DB seems like a good idea, but imo it's a bit too complicated solution.
[0] https://github.com/procore/blueprinter [1] https://github.com/ohler55/oj