PK had to stop working on PKARC because of a C&D request from SEA. He wrote the first algos of PKZIP, which were on par with SEA ARC on compression (and with PKARC on speed), but weren't much better. (And have been deprecated since the 1990 if I'm not mistaken).
Then, the Japanese encoders started to rule the compression ratio (and had comparably reasonable compression times) - LHArc, LZAri, don't remember the rest of the names. LHArc or LHA (don't remember which), had basically the same scheme that PKZIP converged on, except it used adaptive arithmetic coding. PK replaced that with static huffman coding, trading a little compression for a lot of speed, and the format we now know and love as "zlib compression" was born (and quickly took the world by storm, being in a sweet spot of compression and speed).
There's another non-trivial thing that PKZIP had going for it - it put the directory at the end, which meant you could see the list of files in the archive without reading the entire archive! This sounds simple, but back then everyone adopted the tar-style "file header then data" appendable style, which meant that just listing the files inside a 300KB zip file (almost a whole floppy disk!) meant reading that entire floppy (30 seconds at least). PKZIP could do it in about 2 seconds.