I started an Elemental Tactician with Will of Fate and it was the most fun I had even though the build is relying only on WPS and just holding down the left mouse button.
It works especially well too because of the hidden stat on Will of Fate that allows all shots to have 100% penetration.
I’m kind of sad knowing that there is no similar weapon at higher level.
Pretty much what Ana said. I’d suggest taking a look at this guide (specifically the Rifle variant setup) as it should cover what you like (100% penetration and WPSes) and is usable against high-level content.
Other weapons with 100% penetration are the Dagallon guns which can also make strong Fire or Lightning auto attackers.
Coming from someone who has levelled a character like this, the damage conversion and a Vortex of Souls are only really needed during Ultimate (or at least towards the end of it).
Shard of Beronath + the Inquisitor/Necromancer WPSes provide a decent amount of % weapon damage to work off of (Beronath’s Fury + 10/10 Storm Spread shotguns for just over 300% weapon damage in total for instance). Spectral Binding provides a source of Aether which you can pair with an Aether rifle like a Fleshwarped Carbine with Acid Spray/Arcane Bomb/Spectral Wrath/Death Sentence as your resist reduction.
You can easily clear your way through Normal/Elite with it, can’t speak on how well self found does on Ultimate as I had 1-2 gear pieces like a non-Mythical Vortex of Souls ready ahead of time but a good Carbine should do about as well at killing bosses, trash clear will be slower without the penetrating shots.
Edit: Forgot about the Mortality relic for even more flat Aether to funnel through %WD while levelling.