@agentmanatee@Sarpedon All fair enough. I've addressed each point below:
1. I've edited "nearly killed" to just "badly injured"; I was aiming for Rooke's ability to evade the Marine being a combination of having a map that the Marine didn't necessarily possess, setting up a lot of traps (albeit mostly-flimsy ones) in anticipation of the fight, and the Marine not making the challenge literally impossible by instantaneously bullrushing a nine year old boy faster than he could react until he was done being nice. The autopistol and injury dealt was meant to basically be sheer dumb luck, in that not only was Valius in the right place at the right time to acquire the gun, but he surprised an opponent who could otherwise have easily dodged the attack, and then just happened to be aiming the weapon in an appropriate location to cause a relatively severe injury, since aiming for the chest or head would've just had the bullets bounce off of the Marine's ribcage or skull, most likely. Keep in mind that fights against unarmed and unarmoured Space Marines are sometimes used by chapters as part of the Aspirant Trials, and that beating them at the relevant ages is... absurdly difficult, I recall, but not, I believe, completely impossible, especially when the trial isn't specifically to draw blood.
2. Yeah, I figured the weapons were too much. Taking into account what's been said, I've reduced them to just the atomiser and breaching augur on his harness, and the hand-held power axe, which should all be manageable for a single Techmarine. If not, do tell me so.
3. Now, "tone the backstory down a bit"... that's a very vague request which I fear translates to "rewrite most of what you've written", understandably annoying when it's ten thousand plus characters long, and I'd honestly prefer that you be a bit more specific when you ask me to "tone it down". Given that the player characters are highly skilled and superhuman soldiers who are generally more accomplished than their peers, I don't feel like the majority of what I've written is necessarily over the top, and if we compare and contrast the feats of many high-level Space Marines in canon material to what we've got, I might almost suggest that some other PCs are
lacking in significant feats; after all, you'd expect highly decorated war officers to have done quite a lot to get to their current position. Just a thought. That said, I won't be able to make any changes to backstory until tomorrow, since it's late for me, but if anything in particular sticks out like a sore thumb, do mention it.
4. Plasma overheat problem is reasonable enough, and I'll edit that to be less significant. Addressing your comments about his apparent skill, though, and adding on to what I said above, one's position isn't necessarily defined solely by feats, in real life or 40K. Maybe you're the most accomplished fighter in an army without peer, but haven't been promoted to an officer position because that entails a skillset or mindset you don't have; similarly, whilst perhaps Valius' technological accomplishments are quite significant, maybe the way he does things or the way he thinks isn't quite what's needed to be a Master of the Forge, thus a possible reason why Constantine ended up being preferred for the position over him, having a more suitable mindset and skillset and etcetera. And so on, and so forth.