You are using Metamorphosis too late. Meta is a 30s duration, Nuclear Blast is a 5s cast, there's a delay for the tendon lift and then then tendon is up for 18s. From logs you are Meta-ing after the Blast goes off. In between, you need to pop Immolation Aura (which I don't see damage from) and close the range. You're losing probably a global or two there.
Example:
[21:13:04.754] Hideous Amalgamation Nuclear Blast Rainbowsgirl 30664 (R: 76661)
[21:13:06.703] Tapit gains Metamorphosis from Tapit
There are a few other things that you're wasting globals on. You cast Doomguard post-tendon appearing - DG has a 40s duration so can be up before Nuclear Blast goes off. Your first spell on the Tendon is Bane of Doom - it should be Incinerate, to get Shadow and Flame up, since you have a Boomkin. Bane of Doom will still go off if it is cast as your 2nd or even your 3rd global. Finally, if you have your Felguard Felstorm during your first spell, it should be done after you cast HoG/Shadow Flame, and at that point you should pop your Felhunter.
I see you're using Moonwell, but you have that happening right before Meta. Because of the spacing of the plates, Moonwell should actually be cast 20 or so seconds before the Amalgamation starts on the blast - as MWC is about to expire, you snapshot the Mastery with your Meta. Then after the blast goes off, you leap/port then pop aura, and SB/VP trinket/first spell macro. This way, MWC will come up again right about the time the Amalgamation casts the Blast for the 2nd lift (1:35-1:40 ish 2nd Amalgamation kill time). It'll be up for the 3rd lift because of the time to kill corruptions/roll, and for 4th, etc.
Every Demo warlock with Tendon damage issues should master this post:
http://www.mmo-champion.com/threads/...1#post15164572 - afterwards, if you need to rebalance because Amalgamations are taking too long, you can swap out one of two burst trinkets or forgo your filler spam to be weak on 2nd lifts.