which pokemon do you think is highly underrated?

While I don't mean any disrespect towards A!Ninetails, I wouldn't consider it underrated. It's just straight up bad. The only reason it can take Latias's outrage is because Latias doesn't have a very high attack, and it's also part Fairy. And any fairy can take dragon hits like a champ, even the equally as frail Gardevoir.

A poke I would personally consider to be underrated, is something like Exeggutor (both forms). It was a great grass type back in the early days, but now, with FP Venusaur, Breloom, Roserade, Sceptile etc... It's kinda gotten overlooked. But it's stats are still pretty good, and it's a fine option for those for may not have any of the grass types mentioned above. Whereas with A!Ninetails, Even something like Granbull is far and away a better fairy option.

Latias has access to Zen Headbutt, Psychic, and Thunder, none of which A. Ninetales resists. So it doesn't always take reduced damage.

While A. Ninetales is fairly tanky against dragon moves, it's low attack stat means that it isn't putting out much damage in return either. Raids are all about beating the clock, and A. Ninetales isn't much help there at all. If you're looking for something tanky against a Latias with dragon moves, Togekiss, Gardevoir, and Granbull will all do the job just as well as A. Ninetales while also outputting significantly higher DPS.

Now if we're truly looking at something that's exceptionally tanky against dragon Mons with dragon moves, I think that award goes to Mawile who has a unique triple resistance to dragon moves. Unfortunately, Mawile also has abysmally low attack and pretty garbage moves, so I wouldn't recommend it either.

Alolan Ninetales has low attack, weak fast moves, and no exciting charge moves. It can tank a bunch of damage from dragon-type moves, but you are going to be dealing very little damage in return. Aggron has higher attack than Alolan Ninetales. Did you see how much people were complaining about how weak Aggron is when the autoselect was recommending it higher?

To get Alolan Ninetales onto the Pokebattler top 24 list for Palkia, I need to choose cloudy weather and a double dragon moveset. The same choices do not get Alolan Ninetales on the list for Latias because Latias has more weaknesses.

Pkmn Go is a very offense-oriented game, and Alolan Ninetails is better at defense than offense, due to its stat spread. Add ice type weaknesses and it is not even good at defense thanks to many weaknesses given by ice, only fighting being reduced to normal thanks to fairy.