Thank you for proving my point. Just because Chinese grammar isn't as complex as German or English does not mean there is no grammar or syntax, even comparatively.
Every language has a syntax.
If it didn't, there would be no way for people to understand each other. Just because you cannot explain the syntax of Chinese despite your ability to use it does not mean there is none worth talking about. There are ways to form what passes for past tense expressions, there are rules about word order and meaning, question formation, negative formation, etc. Well, you are talking about grammar on two levels. It is no harder for English speakers to master English grammar than for Chinese speakers to master Chinese grammar, at least on the level of use.