Diviner is an underpowered and boring alternative to Aiki. First, it's a single subroutine, which is a poor setup for playable ice. Of the 37 most commonly used ice, only 6 have one subroutine, and 5 of these (Ping, Tollbooth, Funhouse, Turnpike and Magnet) are mainly used for their ability. Vanilla is the cheapest gear-check in the game, and at least forces the runner to dig for a breaker. There's no scenario where Diviner is the best ice you could have. I don't even think there's a scenario where it's a good ice to have. This card would be more interesting if it had 2 subroutines (1: do 1 net damage, 2: reveal the top card of the stack, and end the run if it has an odd cost).
(Thanks to Greasythumb for pointing out that Aiki has not rotated yet).
Aiki is still legal, and it's quite a different card. I agree that Diviner isn't a powerhouse, but not every card has to be. As a gearcheck codegate, I'd say Diviner's main competition is from Enigma, Whitespace and Thimblerig. All those have their advantages and disadvantages.— Greasythumb