The statement is not that AWS is "not good". The statement is that AWS is very expensive, specially for computational tasks, and there are cheaper alternatives around.

AWS is notorious for positioning their services as a way to convert capex into opex, specially if your scenario involves a SaaS that might experience unexpected growth and must be globally available. Training ML models has zero to do with those usecases. It makes no sense to mindlessly defend AWS as being the absolute best service around for a job it was not designed for and with a pricing model that capitalizes on added value on things that are not applicable.