Many of those come from Universes Beyond releases like the Fallout Commander decks or Secret Lair drops like Jurassic World
Its an excellent role-player that creates pockets of potential interaction that didnt exist before, allowing more midrange and control decks to interact with the opponents in the first few turns when mana constraints would be a severe issue
Depends, do you consider Battle of Wits a competitive deck
Can You Respond to End the Turn Effects
Times change, as does what the general public considers appropriate for gaming media
Unless you go through the trouble of specifically placing more +1/+1 counters on her through different means, Arcee, Acrobatic Coupe will always only be a 3/3, while Arcee, Sharpshooter will likely only deal 1 damage each activation