How does the "real thing" make for a better tiling job?
The thing is...the "premixed" makes for a lessor tile job.
The premixed is nothing more than mastic with maybe a little sand added to it to make it look and handle like real thinset. To call the premixed products "thinset" is a real stretch of the imagination.
Mastic takes a long time to dry under porcelain tile, if it ever dries. Under small tiles such as yours it will dry but under larger formats it may never set-up. If the premixed isn't totally dry walking on the tile or getting on the tile to grout can raise bonding and movement issues. It can also cause the grout color to mottle and the grout to cure unevenly. Should the floor get wet or even with frequent cleaning the premixed can re-emulsify and cause grout cracking and tile shifting under foot.
Real thinset on the other hand will bond better, cure/dry as required, stay dry, water or moisture won't effect it after it has cured. It also provides a substantial solid base for the tile as well as being totally compatible with the grout products.
Premixed thinset is a gimmick. The makers offer it and sell it as a one-size-fits-all product and nothing could be further from the truth. It is a lazy man's product.
You won't find any experienced professional tile installer that will use it for anything, most especially a tile floor.