I don't see why everyone is so obsessed with PPA most pvp fights are over within 6 seconds and its still relying on a proc, why the obsession with 1v1 killing everything call incs and pop shield stims adrenal medpack should be long enough for someone to get to you.
Most fights last 20-40 seconds in 1v1 scenarios.
To achieve that comes at a sacrafice of HO, why 5 points to armor penetration of rail shot unless I'm mistaken this soft caps at 65-70% (seem to remember something from the Iron Fist spec in respect of this)
There is no "soft cap" to Armor Penetration. You get the full 90% if you spec into all the ArmPen synergies. Iron Fist is also dead. Even the creator of the Iron Fist spec admitted it is dead. There has been changes to certain Skills that made Iron Fist viable.
Might want to look into that as my info may not be totally correct I havent played in 6 month until recently but there's this nag in my head saying that's correct.
Your info is completely incorrect.
Why not just go the whole AP tree if your scycling Immolate and rail shot you have a guaranteed big hitter every 7.5 seconds which seems a better option than praying on procs for a rail shot that can actually be defended in PVP or outright deflected over a enhanced immolate that I believe is undefendable.
Climbing to Immo and spec'ing into RS synergies for AP is a priority rotation, not just timing Immo and RS apart from one another. Rather, you Immo to make RP free so you can proc a guaranteed crit on RS. Not only that, the RS from AP does not hit as hard (due to lacking ArmPen), and the proc chance is even less than PPA.
I'm honestly not sure what you're basing your opinion off of, because nothing you said is in any way evidential or fact.