I would say that, yes, Stratis does
need to be one step away. That's been the case ever since St. Cuthbert (LN) sponsored paladins.
I would like to point out that if a holy warrior isn't LG, by definition, that's not a paladin. I'm sure there's another name for them ... but, it's not "paladin". It doesn't matter if other people (or products) have used the word incorrectly as a matter of advertisement, or marketing, or whatever.
The Human Paladin of Stratis, by necessary game mechanics, would be listed as something else, if it were not a standard paladin.
The description of the warlord of Thalos, Zadkiel, (who uses the human paladin of Stratis model) gives further insight. In The Ghostwind Campaign, the D&D stats for Zadkiel specifically shows him as a LG 2nd level paladin - of the typical sort; Smite Evil, and all. So, there's that. Also, we know how a paladin of Stratis gets his power:
The Ghostwind Campaign, p11 wrote: The Shield Mother watches over the paladins of Stratis, but even she cannot heal their souls.
So, we know that she's LN. That pretty much precludes the paladins from being CG.
have grown up CN and later become LN, but, so can anyone. That would be just the purest form of speculation. Without any canon hint for that, I'm not comfortable making things up out of whole cloth.
A very minor nitpick: there's nothing that really characterizes the murder of Stratis as "assassination". The original engagement may've been an ambush, but, my personal opinion is that casting it as assassination puts it in a light that really isn't the case. Especially since those who attacked him thought they were defending humanity from
Stratis. They thought that he was the one creating
the wars. IMO, the lesson we learn is that humanity would still be fighting, even without someone to lead us into war. We'd start fights all on our own.
You're certainly not the first I've heard use the word in conjunction with Stratis. But, I think it's more accurately described as "murder" or other things, but, not assassination.
I'm going to assume that the "action that might be interpreted as chaotic" to which you're referring is his dying curse, and spreading his panoply. I would point out that there's nothing chaotic about laying a curse on someone. Not the act, itself. A person's motive can be argued 'til we're blue in the face. But, the act
of a curse is actually very lawful. There's a specific set of rules that has to be followed. There's always the escape clause, the set of fulfillment clauses, a process for removing the curse - everything about how a curse works is lawful.
Even the act of dictating the successor to the "throne" of the War God -no matter how difficult to attain- is a lawful thing. Trial by Combat is still a ritual and is supported by millennia of tradition ... so, it's not chaotic, either, it's lawful.
Can a Chaotic creature take Lawful action? Sure they can. But, by Occam's Razor, the more likely answer is that he is Lawful.
These are all good questions, though, and lead us to explore what we known of the setting.