No, we haven't. You can start at any byte in a UTF-8 document and resume reading coherent text. If you start reading from the middle of a multi code point sequence, then the first couple of glyphs may be wrong, for example you may see a lone skin tone modifier rendered as a beige blob where the author intended a smiley face with that skin tone. But these multi code point sequences are short, and the garbled text is bounded to the rest of the multi code point sequence. The entire rest of the document will be perfectly readable.

Compare this to missing a code page indicator. It will make the whole section until the next code page indicator garbled. The fact that you're even comparing these two situations as if they're the same is frankly ridiculous.