Out of the 4 factors they used, the only one that has actual meaning is the #1 album, which all 3 have, so it's a useless factor anyway. I guess social media power (not just Insta) could also be somewhat acceptable but eh.
Based on real factors, such as vocals, dancing skills, stage presence, catalogue, distinctive style / musical identity and potential for the future, Ariana would be ahead and Demi and Selena would be battling it out for runner-up, cause one is more talented but the other seems to resonate more with the GP so the next few years will be telling.