Archetype ascension is mechanically weak implemented and here is why and how to fix.
Ok, lets talk about ascension. More precisely: during play ascension. Meaning, you play a Tier 2 Campaign and at some point the Campaign becomes Tier 3 and all the characters ascend using either archetype ascension or ascension packages. I consider archetype ascension to be narratively inferior to packages and mechanical sloppy implemented in general. Today, I would like to talk about the second part only. We will check the current rules and what needs improvement. I will finish with my own proposal for how archetype ascension should mechanically work.
What is it
Archetype ascension allows a character to move to a higher archetype within its faction. Best example is probably the Astartes Scout (Tier 2) that becomes a full fledged (Tactical) Marine (Tier 3) with power armour and such. But there are other valid progressions, like an Inquisitorial Acolyte (Tier 1) becoming an Interrogator (Tier 2) or a Tech Adept (Tier 1) becoming a Tech Priest (Tier 3).
The current state
Let's recap on the rules (Core, pg. 155) for archetype ascension:
You need to be Rank 3 and have earned at least 80 xp,
then you select your target Archetype.
You need to bring (via spending xp) attributes and skills up the the requirements (so to say) of the target Archetype.
Then, surprise, increase the Tier on the sheet.
And finally, you become the new archetype (see below), aka you gain (read: add) all the following benefits:
add the new archetype ability
add the new wargear
add the new influence bonus (not clear here if that replaces the one but RAW indicates add)
add etc. (whatever that means) maybe the keywords and corruption (if any).
It is noted, that you "You do not gain any Attribute or Skill bonuses from the new Archetype, and retain all of the benfits from your previous Archetype." Which is like everything as the attribute and skill stuff is not a bonus but a requirement already fulfilled with (3).
What's the problem
It's to strong as you gain benefits without paying for it. It also leads to strange combinations compared to "fresh archetypes". Let me explain.
First, normally, an archetype has a cost that is computed by the accumulated cost of the attributes and skills it requires (and bring with it) plus its (Tier-1) x 10. Like, you pay for attributes and skills and get Keywords, Ability, Wargear, Influence and sometimes corruption for the raw price of e.g. 10pts for a Tier 2 character. The costs do not always add up in the books but I assume this is due to calculation errors. So lets assume the cost stated are correct.
That cost is "missing" when archetype ascending. Lets compare 2 chars of a Tier 2 Campaign that moves to be a Tier 3 Campaign:
Brother Shadow, started as Tier 2 Scout and Ascends to a tactical
Brother Nooby, fresh from the academy (the players previous char died and they make a new one) making a Tier 3 Tactical marine
Even when we dismiss all the additional gains from (5) above, Brother Shadow would have paid 10 pts less for the same final archetype.
When switching the archetype, not only do you gain all the new stuff but you also (unjustifiable IMO) keep your old stuff.
Taking the example marines above, this leads to two marines: one that remembers his scout training and one that does not. Why? I see no narrative justification for this.
Proposal for improvement
We will make 2 changes. We will (a) add a tier diff related cost and (b) replace stuff instead of adding them. While (a) is easily priced: (newTier - oldTier) x 10. (b) is a little tricky. But with the watchfull eye of the GM and some common sense we will get there.
The archetype (aside from stats) consist of there benefit:
As you progress within your faction, the new Archetype might mostly have a keyword set that contains the old archetype ones. That said we will go with:
You gain all Keywords from the new Archetype that you do not already have.
I mean, this is identically to the current approach. One would obviously not gain
[Chapter] again but remain their current one.
As stated its weird to remain with you old ability. If you like to still have them, you should use ascension packages instead of archetype ascension IMO. Therefore we scrap it. You replace the archetype ability.
Here to we would replace the gear not add it. We could also add it as it's mostly not so tragic as the gear is of "lesser" tier and thus not a got use in the new tier anyways. There might be exceptions. Mostly Armour and Primary weapon is to be replaced. Then again see in the individual cases.
Remove all Weapons and Armour granted from your old Archetype. Retain other gear (GM may veto). Then add the wargear of the new archetype. The GM may rule that you retain all your old archetype equipment.
You do not gain both, you should only get the new one, representing your current status.
Replace the influence modifier with the one of the new archetype.
Those changes would lead to a world where Brother Shadow is on equal footing with Brother Nooby.