It's common knowledge that Caine2 has fallen far from the monster he used to be and is now rarely played in any kind of competitive scene. But what I think is less-discussed are the reasons for this. Sure, the meta has changed, and yes - the rune shot nerf did hit him hard. But I believe the main reason he's no longer as good is a different one: themes.
The support models I always used to bring for Caine were Reinholdt, rangers, and Gun Mage Captain Adept(s). Since he's come out, Bastian Falk is also a good option.
Since the advent of themes, you can only get rangers in Gravediggers, and you can only get Falk and GMCAs in Sons of the Tempest. Ace is a great support model that Caine can always take, as the thunderbolt and shadowfire are priceless assassination-enablers. But the loss of GMCA flares and ranger mark target really does hurt Caine. I'm feeling like his feat is often best used in conjunction with Falk's runemarked shot to take out heavies or severely wound a colossal. (Avg dmg for the 9 shots with rune marked on an ARM19 colossal is 54)