Wall of Text Ahead!: I'm really only play Sharpshooter so I have some strong opinions regarding the class' weapons:
In their current form, yes, the MK23 is a a more reliable sidearm than the HC, though it takes 1 extra headshot for both Sirens and Husks on 6p. ; however, what we should be looking to change isn't the HC, but rather the .44 Magnum and the MK23. Most people (or at least I'm assuming most people) were satisfied with the power of the HC before the introduction of the MK23 (since the .44 Magnum was already at 2 kg. allowing both to be carried), but since the MK23's are now an actual part of the game, the HC all of a sudden became "too weak" of a weapon despite it not having been changed (which to me makes absolutely no sense at all).
Here are my proposed changes (Which I'm sure many people may disagree with. Feel free to since these are just "Proposals" or "Suggestions"):
-Handcannon: Leave as is (Same damage + same ammo capacity + Fire rate + Recoil; Same everything. Don't touch it)
-MK23: Remove the penetration entirely + increase recoil (by a lot; like double or so) + lower base damage (to the point where crawlers must be dealt 3 body shots) + increase headshot multiplier (So that in terms of damage dealt by headshot, it becomes as powerful as the HC) + increase weight to 3 kg (Dual Wield remains at 4) + decrease total bullets per magazine to 10 (Dual Wield at 20) + decrease total ammo to 140 (from 144) + Reduce base price to 400
-.44 Magnum: Give it the same damage and penetration as the current MK23 (Now players must triple headshot Husks and Sirens), but keep the total magazine capacity, bullets per magazine, fire rate, weight, and recoil as is + Reduce base price to 400
Now here are some explanations for my proposed changes:
Handcannon: The Handcannon was balanced before the introduction to the MK23's, and have not changed since then, meaning that it is still balanced today. If a Sharpshooter misses the headshot on a crawler, then they should be penalized that extra 1 ammo cost as they are built to "Land Headshots". If they miss too many headshots, then they'll have to compensate by switching between the HC and 9mm. If Sharpshooters could quickly remove Crawlers easily despite sloppy aim, then we'd be blurring the roles between the Commando and the Sharpshooter. It's similar (this is just an example; you may disagree) of how the M99 AMR once made Demolitions less appreciated since the Sharpshooter was able to more easily dispatch multiple Fleshpounds without the drawback of the heavy smoke that the Demolitions had to deal with.
MK23: My many proposed changes of the MK23 are so that it becomes weakened (so as to not outshine the Handcannon), yet create a weapon that is unique to and functions very differently from its .44 Magnum and Handcannon counterparts. If any of you have played with me before, you'd know that my preferred weapon is the M14 (and that I dislike penetration damage). These changes make the MK23 a lesser version of the M14 with lower weight so that it may be carried as a sidearm to the Xbow (for all you Xbow users out there). By making the MK23 weaker in terms of base damage (to the point of 3 bodyshotting a crawler to kill), we make it less viable for sloppy Sharpshooters, thus forcing players to improve their aim as they should be doing as "Sharpshooters". By having it deal the same damage per headshot as the Handcannon, it functions similarly to (since it is weaker, not exactly like) the M14 (except for stunning Husks) for headshots on specimens weaker than the Scrake, Fleshpound, and Patriarch on 6p.
.44 Magnum: In my proposed changes, I did not change the weight (still permitting the .44 Magnum and MK23 to be held at the same time alongside the Xbow), but now if one wants to dispatch Sirens and Husks, they'd probably want to switch to their MK23 instead (to preserve their Xbow bolts).
Overall effects of these changes:
The .44 Magnum and the MK23 (now an entirely new kind of weapon) function similarly to a single Handcannon except they now require a lot more switching but have almost 3 times the total amount of ammo as a single Handcannon. Handcannon is a cheaper alternative and requires less switching but requires more accuracy to compensate for the lower ammo count.
Now the Sharpshooter needs to shoot more accurately and land headshots as it was "already designed to do". Any proposals that change the Sharpshooter to play with bodyshots is diverting the class from how it was meant to be played.
Remember that at the top I said that these were my personal "Opinions" so if any of you disagree with anything, then feel free to say so, so long as you either provide reasons or your own proposed changes.