https://en.m.wikipedia.org/wiki/Jack_of_all_trades#Other_quotation_variants

The phrase with the "master of none" element is sometimes expanded into a less unflattering couplet with the second line: "but oftentimes better than a master of one" (or variants thereof), with some sources (who?) stating that such a couplet is the "original" version, with the second line having been dropped. Online discussions attempting to find instances of this second line dated to before the twenty-first century have resulted in no response, however.

I've never in life heard someone say that 3rd line. It should also be noted that even on the Wikipedia article about this speculation, they don't link to a single source. I believe that line is a purely modern invention.

Even in the post I was replying to Jacksilver says "The “But master of none” seems to be a latter addition". The fact that it's a later addition is mentioned in the article as well. How could 'The Full Phrase' include a later addition if it was "the original"?

If the intention is to be the same as the original meaning, it weakens it. Why throw a little shade in there (master of none) if you are tying to compliment someone?

Even if that were 'The Full Saying' leaving that part off changes the context, so "Jack of all Trades, Master of None" absolutely has a different connotation that 'The Full Saying'.