Clarifying my thoughts:
As background, I didn’t design the bugman praetor, but I did sponsor it with a high-level pledge. The primary goal of the class is to add a four arms ability to ACKS. Yes, that’s really, really hard to design. There’s very little left that I would like to add to ACKS that is easy to design. If this is impossible, then I am very sad that playable Green Martians or Thri-kreen can never appear in ACKS.
Yes, XP costs are not a panacea to “balancing” anything we might imagine. I don’t like the word balance - it’s one of those words that means different things to different people, instantly generating conflict. I aim for compelling play experiences over time. I hope that players have a really tough time deciding what character they will try to keep alive through a campaign.
Because of the inherent challenges of the bugman praetor, I think we have to compare it to something like the bugbear character class from Axioms. Starting with 3d8+1 hit dice is clearly superior to any core class. As Judge, I doubt I would ever have a bugbear PC start out with normal humans. More likely, either the bugbear class would “unlock” at some point in the campaign, or I would start a campaign at higher than 1st level.
From a “feel” view point, I think starting the bugman praetor with a low AC which increases at perhaps levels 7 and 13 (bladedancer-like) would make the class more compelling. I don’t know that I want to rule out armor, but I lean toward armor being not the best choice, and really expensive to create or re-size for a six limbed creature.
In summary, the bugman praetor is a challenge, but I think the ACKS community is up to the challenge.