You mention skilled gunslingers being able to pull off certain feats, and in this system they can - because being a skilled gunslinger is represented via the Deadeye shot talent - if you choose not to invest XP into an option that represents your skill at arms, then you can't complain about not being able to pull off complex manouvers without spending more time doing so.
I would have thought that much was obvious…
Well, the problem is that even with all these talents, they still can't make that Called Shot to the head without a comarative loss of bonus. Because they cannot use the Aim action with the Called Shot on one round.
Sure, they can make a Called Shot without penalty, and hit a Head at base BS (assume normal range).
But they could make an Aimed (+10) Standard Attack (+10) attack vs the flying head (-20) for the same net modifier (0), but then gain the bonus for Accurate weapons (which they likely would have, being artisans of the gun).
I think it is strange that the other shooting actions were reduced from Full to Half actions (Semi/Full auto Burst), but Called Shot remained a Full Action.
The change from the original DH rules (which happend with Rogue Trader) was quite a nerf, as they kept the -20 penalty but also prevented a mitigation of this with Aim. I guess this was to counter the increased damage done by Accurate weapons (which was introduced in the Errata, and so was not originally DH RAW), and to prevent snipers form one-shotting one enemy per turn. But I don't think that was necessary, as the heavy gunners or explosive users could easily put down more than one enemy a round as well.