This is the second time I see this comparison, and it remains unfair.
For one, the applicability of Presto surpasses Finger. Works on constructs and undead, at least. Also has no SR check.
The DC is also ridiculously easier to get.
This is more of a no-attack-roll, (working) Ranged version of Coup De Grâce (because the DC on both abilities will be similar), that requires absolutely no setup, or a T5 replacing a level 15 ability, Hurl Through Hell (that's also on a 25 second cooldown)
I agree that both the AP and mana costs could be given a second glance, but the cooldown is fine for the effect given, if we compare it to similar abilities and not Finger of Death.
Comparing 2 things doesn't imply they need to be exactly the same to be a fair comparison point.
The point I was making is, this T5 enhancement is the only unique draw to AT's T5, and it does not succeed at being an effective reason to use the tier 5 from AT.
Killing 1 target every 30 seconds, no matter how easy it is to build around or optimize the DC, is just a neat trick, not a significant part of how the build functions.
If they want AT tier 5 usage to be limited to only builds that go 20 AT, then they've nailed it.
What they have built here is ultimately going to be extremely niche and probably largely unused by the player base, like so many other archetypes have been, without some substantial tweaks.
Personally I really enjoy when new content has cool ways to build around and incorporate into new ideas, but AT seems relegated to 20 AT, and that build is going to be mediocre at best.
If Presto was 15 second cd, you could at least use it reliably about once per pack, which would be a bigger draw. I maintain that a chain instant kill (with a nice chain poof animation and sound) would be super fun and interesting, and something people would salivate over, rather than say "oh yeah this is neat".
Ultimately that's what game design is all about: creating concepts that excite, not just things that are ok and technically work.