Pitch accent isn't necessary either. Just like English, Japanese has many different regional accents that sound different, yet people from one region can still understand people from another.

The difference is that people write with more homophones than they speak with, just as written English is different from spoken English (more subtle word choice for brevity), but that is not necessary for communication, and written language can adapt just like children's books which don't use Kanji.

Hanja worked fine in Korea, and there still remain a contingent who insist on it, just like there remain people who insist that Kanji is necessary. The fact that people born blind can speak and understand both languages shows this to be a lie.