Is it a good practice to use index hints in production code?
Although your question is about MySQL, Brent Ozar has a good article on this topic about SQL Server.
Generally you want to avoid it for a few reasons, data/stats/indexes can change in the future and then using that index would be bad and hurt performance instead. But if nothing else will solve this, then you can always use it and document it for the future.
I've used RDS a few times and it can be night and day different than using a database on a machine I've noticed. Are you using one for development and one for production? Or what's the different uses for the two? And do both have the same amount of CPU/RAM?