The problem with Arena vs. Bob is that Bob is A: 2 mana, B: a 2/1.
It's both faster and has a self contained clock. The life loss is a nonissue. I don't know much about Modern though but in Legacy Bob is only really played in Team America (which isn't really a thing anymore) and maybe UB Faeries (which was thing for all of a really short time). It does see play in some of the more uncommon decks like Deadguy Ale and Team Italia but it's far from being the best card in the deck.