I had a very significant reason for not using the Desolator: I did not know about it :). I tried so hard to make the Vortex work and never had an idea to search for other similar weapons in Grimtools. And they exist. And builds with Desolator are present here - for example: https://www.grimtools.com/calc/nZo6xMdV
Why is this stat hidden on weapons? Ehh… mockery.
(…a few hours later) [1.1.4.2] Skorkh, Railrocketshotgun Pistoliero - DW Ranged Fire&Lightning Dagallon Justicar Purifier (no greens, Gladiator) https://www.grimtools.com/calc/D2p653KZ
Now it takes <9 minutes with 4 blessings 
https://youtu.be/-WSMsLYcBp8
With 3 blessings and 1 banner it took 8 minutes. But I am not used to banners, so the result might be non-representative.