One of the big things to note is that Sparky plays very basic decks, with few complicated cards and combos. Rules-based AI could definitely play at a basic level using a beatdown strategy, but give it some sort of control/combo deck and it would struggle.
Hearthstone allegedly had bots hit Legend rank back in 2014 playing Aggro Shaman. Those were believed to be pretty simple rules bots, so yeah +1 that approach gets you pretty far if you have decks crafted for it.
