Strong Imp not so strong after all

So, 18/53 got some noise early on in 3.3 as being the destruction spec of choice. Then all of a sudden it wasn't on the EJ compendium anymore. What happened? This happened:

 

Doesn't look put up such a good showing, does it? What happened? 18/53 joined 40/31 and 41/30 (though not so quickly) in the communal grave I call buried by scaling. Imp scaling is awful, buffing the imp in this way is only a temporary thing. The logic that 4 piece tier 10 would magically make so much more difference for 18/53 also didn't hold up for long - had anyone stopped to think about it, they would have seen the same fact without tests needing to bear it out.

18/53 outperformed 13/58 in the old ToC gear profiles, but not ICC ones. However, it's rise to attention wasn't even so warranted then. Why? It outperformed in the EJ 300 second 5 minute benchmark, but just like 3/13/55 before it, it didn't hold up in, say, a 360 second test (6 minutes). In my gear going into 3.3, 315 seconds was enough to put 13/58 back up on top.

Issue at hand is how simcraft handles life taps. It doesn't distribute them evenly for destruction, it life taps to maintain the buff, and then when it bottoms out, life taps for mana as needed. Now, this is where ISL comes in: It can sustain itself for a long time this way in TOC gear profiles, it'll end a 300 second benchmark around 40% mana. 3/13/55 and 18/53, though, hit this after less than three minutes, meaning their high DPS starts to wane after that point. 5 minutes is a short average for fight lengths, few fights in ICC resolve themselves that quickly, and fewer still are likely to in heroic. 13/58 also has substantial flexibility in stats. You can see where imp and immo glyphs line up with LT in the ICC BIS profile. Don't go running to the auction house just yet, if you're coming from a typical TOC gear setup, LT is still the best, nothing's changed there. However, things start to change when you drop under 400 spirit, which you're going to if you're gearing for personal DPS in ICC. Demonology has to do some unpleasant things to itself to keep spirit up for demonic pact purposes.