Hisoka was really not an antagonist during the Exam though. He was certainly a force of nature meant to make things more scary and dramatic, but really, he didn't fill the roll of an antagonist. He didn't really stand in the way of our main characters. Hell, he helped Leorio pass the first phase and gave Gon his badge back.
Illumi really wasn't a character until the last two chapters of the arc. He did fuck will Killua, but for such a minor roll, it's hard to call him a mejor antagonist at this point
In the Heavans Arena, Hisoka was the mejor fight goal, and you could say that constitutes being an antagonist. However, it's nowhere near what someone like Chrollo, Genteru, or Meruem were.
Calling Feitan a mejor Villiam is comical. Hell, Paku had a much bigger role. Razor was also a 1 volume guy they had to beat in a fight. Important, but hardly a main antagonist.
The Royal Gaurds mostly took a backseat to Meruem, with the exception of Pitou, who killed Kite and caused Gon's tragic end. Meruem (like Razor) was just a big dude they had to fight. Pouf was really an antagonist to Meruem and Komagi, not the protagonists, so he doenst count either.
Illumi was an antagonist in the Election arc I guess. Pariston too I guess? But neither were that big
Which leaves us with 4 specialist main villians (Meruem, Pitou, Chrollo, Tse) and 3 non specialists (Hisoka, Illumi, Gentheru).