You're forgetting the difficulty of learning the elaborate system of honorifics, without which you'll be unable to talk to a native speaker without insulting them. The title of this book gives some idea: https://www.amazon.com/exec/obidos/ASIN/4770016247/ref=nosim...
While that is technically true standard 敬語/honorifics (です/ます and a few word choices) aren't really that complicated.
There are additional levels of honorifics which can be far more complicated but (outside of workplace honorifics -- which you will need to practice if you will work at a Japanese company) native speakers usually get some kind of training in how to speak in that exceptionally formal way (the kind of keigo used in restaurants is sometimes criticised for being "incorrect" Japanese and is called バイト敬語 -- usually service workers literally get handed a manual which explains how to interact with customers using this form of 敬語). If you or I had an audience with the queen we would probably also get some kind of training in how to politely speak to her.
Finally, if it's obvious you're studying Japanese and you drop a です or ます the person is quite unlikely to be insulted. Especially if it's not someone who is your superior at work.
Just to relate back to the original point of adopting a universal language, I would guess that if any language were adopted as a world-wide language, then things like honorifics and formal-informal distinctions and gendered articles/nouns would be dropped pretty quickly.
There are additional levels of honorifics which can be far more complicated but (outside of workplace honorifics -- which you will need to practice if you will work at a Japanese company) native speakers usually get some kind of training in how to speak in that exceptionally formal way (the kind of keigo used in restaurants is sometimes criticised for being "incorrect" Japanese and is called バイト敬語 -- usually service workers literally get handed a manual which explains how to interact with customers using this form of 敬語). If you or I had an audience with the queen we would probably also get some kind of training in how to politely speak to her.
Finally, if it's obvious you're studying Japanese and you drop a です or ます the person is quite unlikely to be insulted. Especially if it's not someone who is your superior at work.