Honestly, the Surge abilities are very much similar to the weather abilities in Drought and Drizzle, and I imagine that GF will eventually go the route of giving these signature abilities to other Pokemon as Hidden Abilities, just as they gave Drought and Drizzle to Ninetales and Politoed respectively. I also believe that there is room for exploration in the terrains still, as some unique abilities heavily involve thier usage and different role archetypes such as hazard setting and revenge killing still have not been fully explored with these abilities. So, I think that giving it a Secondary Ban is the route we should take.
Beast Boost also has some unexplored potential, as this ability is very much reliant on stats and EV investment. Celesteela has really been the only one to capitalize on this, since most of the other UBs have incredibly crazy stat spreads which only ever boost one stat upon its activation. I think there are some routes we could go with this, such as a more defensive usage, and support a Secondary Ban.
Soul-Heart has already been elaborated quite a bit on, and Deck Knight pretty much hit the nail on the head for my opinions on it. It is far too easy to activate due to the passive KO boosting, and Beast Boost also acts as a far more safe alternative if we want any sort of Special Moxie. There is also the optics issue, as the only other Mythical Exclusive ability in Victory Star has already been banned, and I see no reason to unban it. It would be far too weird if we kept one banned but not the other, so I support a Total Ban.
Stamina is slightly worrying to me, as it has the potential to get out of hand very quickly. For example, if given to a largely specially defensive mon, it could be able to switch into a weak special attack and get it to activate, getting a buff to its defense. It could then very easily snowball out of control and become a very hard pokemon to get through. Of course, CAP does have HazeHawk and multiple pokemon capable of Hazing and Phazing, but the point pertains no less, especially if it can threaten these mons. I think that it should most certainly get a Secondary Ban at least.
I support the philosophy of common sense being used in terms of flavor abilities. Most people can recognize what abilities have competitive usage based on other viable pokemon in the metagame can effectively use these abilities. For example, people could assume that giving a CAP Moxie or Aerialate as flavor is a bad idea, based on DD Mence and Mega Pinsir respectively. For the abilities that are more disputable, such as weather boosting abilities in the line of Swift Swim, thos could be handled case to case. Most people at this point uderstand that Legendary Abilities are pretty much off the table in any sort of ability discussion, so I see no need to enforce this for the third time when it is obvious that these mons will not get these abilities anyways.
