Agree, theres also dive, liquidation, whirlpool, theres too many possibilities for what can happen, and that goes for more than just palkia
Theres more than just a few nitpicks to have with that guide, mostly they only focused on best attackers of their type without considering the relevance of each type against legendaries. YEs Raikou Mewtwo and machamp are strong, but when you look at the legendaries of gen IV, they're not good agaisnt the vast majority (yes shadow ball mewtwo's good againt 5, but tyrantiar still handles all better with STAB and resistances). It seems that they did fall into the mentality of "whats been good/relevant since gen 1 will always be good/relevant" (something I plan to actually make a post on here about) Those assumptions really cant be made with the same level of certainty that gen 3 because of just how different Gen IV's legendaries are they do share types with pervious pokemon, but different type combinations that make certain types better against them (for example dialga and palkia are both dragons but arent weak to ice, and Heatran being steel but ground being better against it than fighting)
The meta of gyms will also really chang,e as up till now, everything that had the highest tank stats was generally weak to fighting, hence why machamp was king, but gen IV offers a lot more diversity in tanky pokemon that arent weak to fighting, and other common gym clearing types
Yes these assumptions were made only using current moves, but that is also a problem. That is also neglecting all the possible new moves that can be added, the gen IV pokemon have stats and the potential for moves, something gen 3 didnt really have to the same extent.