My bad, but like I said, I don't have my book here right now. Ambidextrous is BS/WS aptitudes, so we lost there, that's for sure…
Ambidextrous is also T1. You "lost" a whole 200 XP there.
Also "….Agility, which is crucial for a melee specialist….."
Again, that switch of aptitude made the ST a ranged specialist, not a melee one; the only way Agility is important now is that a storm trooper must now rely on dodge to get out of harm's way rather than the more potent Parry.
How is Parry more potent than Dodge? Yes, a decent weapon can grant you a few points, but I've yet to see someone parry a lasbolt outside of Star Wars.
IMO, the weapon specialist is the allround guardsman with some added shooty-ness. The Stormtrooper is the shooty specialist with some added allroundness, but essentially, that's their job. They are hunter-killers in perfection - they go somewhere, shoot something and move back to base. Crawling through mud, hiding for weeks and digging trenches are things that happen to other guardsmen.
Also, yes, doctrines that provide more aptitudes are extremely powerful. There's hardly a system out there where learning cost reductions are not among the most powerful traits. Doctrines that provide you with a greater supply of expendable stuff are pretty nice, but reduced learning costs will always more than pay for themselves unless the system is heavily reliant on equipment over character skills.