This is in no way unacceptable. I am assuming you purchased the controller based on its price as I can't think of any other reason why you would. There are a few reasons why Gemini gear is so cheap but above all reasons the one affecting your current situation is Gemini does not have a partnership with Serato thus no native connectivity. I can also assure just as there never has been one there never will be one. To put it bluntly they are two different standards.
There is nothing wrong with going with the lower end gear if that is what suits you but you can't expect higher end functions out of lower end gear.
It says right on the box that it works with VDJ so there should absolutely be no surprise that it doesn't work with Serato. You CAN map your controller to SDJ as long as it supports Midi. Obviously the functions it controls will be limited but remember you get what you paid for.
Lastly (and this is the hardest part to say) the gear Gemini makes is not what anyone would call quality gear. This would cause nothing but headaches for Serato if they decided to support gear that will eventually fail. At the time of said controllers demise the fingers would then be pointed at Serato as well as Gemini which would in turn give Serato the same reputation Gemini has earned themselves.
The majority of this is based on opinion but I promise you if it is not entirely accurate it is not far off.