If you want to stretch things like how Gen 6 were RPG classes, then Rowlett is Archer, Litten is Monk/Martial Artist, and Popilio is Bard... but that is IF this is real. and Iam pretty convinced that that leak is fake as fuck.
1. I predicted that Rockruff would be a Wolf... but NOT A WEREWOLF. I am still holding on to the theory that Rockruff is based on the Makami. A mountain Wolf Spirit thing.
2. Litten seems to be a special attacker, not a phys, so Despite my obvious bias towards Luchadors being awesome, I don't buy Litten being a luchador based on Tiger Mask or anything like that. I am certain that they will keep the themes of Circus performers and Litten will be a Tiger who jumps through flaming hoops. Litten also seems to be the Mind pokemon due to the Sulfur Alchemic theory thing. Also seems likely due to it having a lot of emphasis on spitting fireballs, where the other two have emphasis on physical properties as well as special. All starters are based on Mind, Body, and Soul.
3. I can guy Rowlett being an archer... but I will wait until that gets a much more solid piece of evidence. Theorists think he is Soul due to his affinity with the alchemic symbol for salt. Remember, it kicks and throws feathers.
4. Poppilio is an acrobat. So how the flying fuck does an acrobat turn into a Siren/Bard? That doesn't make a lick of sense. I can somewhat buy Rowlett being an archer, and I kinda am okay with Litten being a bad ass luchador... but I cannot buy Poppilio being a siren at all. It is especially odd since all the starters have emphasis on being either Nonbinary or Metrosexual in design. With some exceptions... but none of the ones that lean towards one gender over the other go overboard in the slightest. The Supposed litten starter is way to manly and do I need to mention how holy crap girly the supposed Poppilio starter is supposed to be? I don't buy it. Also remember, Popilio is supposed to be agile and acrobatic, not a supportive special attack. It is also likely tha Popolio is based on body due to it's ties to mercury.