Let's just say with a bard and BV with a buffed Fester x2 + deathflare, it's really that good of a burst that it will cover up the 2pf/1f opener 100 potency loss. If only there was a calculator to sum up the GCDs + total potency gain of each opener.

to see it somewhat realistically:
DWT > R2 (2.4 gcd)> Aether + Enkindle > R2(2.4 sec gcd) > 3D > R3 (2.4 sec gcd) > R2 (2.4 sec gcd) > Fester > R3 (2.4 sec gcd) > R2 (2.4 sec gcd) > Deathflare == (2.4 x 6 = 14.4 seconds out of 15 secs with absolutely perfected execution) I'm not including the R2 prior to DWT which i know it will clip the next cast so it's a 15/15 with 0 ping or no lag

DWT -> Tri-D -> Fester [10-11 secs left on pot] -> R3 (2.4) -> R3 (2.4) -> R3/R2 (2.4) -> Fester [1-2 secs left on pot] -> Deathflare [before pot ends] == (2.4 x 3 = 7.2 secs out of 15 secs) means you can squeeze 1 extra ruin 3 and endure some clipping with a full pot duration.

In this scenario I'm assuming the recast time is 2.38 or 2.4 seconds. Am I missing something? Still trying to understand it. ;w;