People do learn in different ways and different languages pose different challenges. Example:
My wife and my Hebrew:
Wife: fluent speaking, sounds like an Israeli (every Israeli she speaks to thinks she is a native) fluent listening, understanding, conversation, news, tv, etc. She can of course read, but the more formal tone of written language in books, newspapers and academic articles is hard for her.
Me: The exact opositte. OK speaking, like I can get around Israel without a problem, but a lot of common, everyday nouns I always forget for some reason. People on the news tend to speak to fast for me (as do many Israelis when they just go on and on). But I can read the real heady stuff, academic articles, books, etc. My grammar and spelling are much more correct than my wife’s (or most Israelis who speak quite incorrectly). I have taught Hebrew at both the graduate and undergraduate levels…taken immersion, lived in Israel, etc. But for the life of me I cannot become fluent in “street Hebrew”. However, if you want me to break down the development of a word from biblical, through rabbinic, to medieval and then modern usage, giving all the nuances, then I am your man. if you want directions to the grovery store in Hebrew, ask my wife
So now thinking of Chinese:
My wife hears a word, remembers how to say it, tone, meaning, etc. Me, I gotto see the character, look at the makeup of the combined radicals, etc.
So my wife is much more of the “absorber” type, me…my brain simply does not work that way. So for learning Chinese, unfortunately, it takes quite a lot of drilling down with the characters and vocab. For someone like me, Chinese does pose more of a difficulty…or perhaps not a difficulty but there is an extra time commitment due to the character system.
So essentially, I think some languages are ‘harder’ (takes more of a time commitment) for people and some are ‘easier’ (less of a time commitment) for others.
If you have lived here ten years and cannot hold a conversation, however, I think that says more about your priorities (whether you really cared about learning the language or not) than it does about you as a teacher. Not all good teachers are good students…