While the Weathered 10mm pistol can be modded it lacks the meshes to display them in game. Just dropping the "Weathered" is the best thing do. It'll cover all the game copies across all the platforms, both current pre-order and future sales.
Still think the Trail Carbine should be on the list if the equally broken Brush Gun (for PC) is there. It's the perfect compromise between short range VATS and distance free-aim sniping with little hassle for both ammo and repairs.
"Ratslayer" and "Varmint Rifle+All mods" could also use a mention. I've put down many Legionaries with those two guns firing .223 rounds, or 5.56mm HP to the head, on Normal Difficulty.
I also haven't experienced the problems you have with brush gun. Sometimes it locks up and I can't fire, but that's only happened 2 times for me. The vats problem hasn't happened at all for me.
The real issue is that none of those weapons (ratslayer, trail carbine, etc.) come anywhere close to the power of gobi, sniper rifle+ or even this machine. Taking down legionnaires in 1 shot is easily achieved by... i dunno... 10 or 15 weapons in the game? That's not really a good benchmark. So I don't really feel it necessary to mention them.
Let's look at Ratslayer. I hate to say it, but Ratslayer is an absolute joke compared to Sniper Rifle+. Ratslayer using 5.56mm, Armor Piercing (probably it's best ammo) does not come anywhere close to the level of carnage you can make with a Sniper Rifle+. Let's say you have a target that actually has 15 DT or less. Then you'll be doing x0.95 of 23 damage, which is 21.85 damage. If you've got the proper setup, you'll crit 100% of the time, so you'll deal about 54.625 damage.
I'm sorry to say, but Sniper Rifle+ does 62 damage with regular .308 ammo out of the box, with no crits. It already wins. If you use .308 JSP with the same gear as our theoretical Ratslayer user is, you'll be doing 232.5 damage per shot. On top of all of this, Sniper Rifle+ has a faster rate of fire, so over 2-3 second span it's going to be doing even more damage. Ratslayer is so far behind, you just can't see it anymore.
Conclusion: If you really want to snipe things, Gobi and Sniper Rifle+ are the answers. There is nothing better.
As for trail carbine, it does benefit from the Cowboy perk... but even so, it still doesn't beat out This Machine. Trail Carbine will get a +25% damage boost, so each shot will deal 56.25 damage. This Machine already does 65 damage out of the box.
Now, .44 Magnum ammo is not nearly as good as .308, because it doesn't have any hand loader version from what I can tell. I have the Hand Loader perk, yet there is no hand load option for .44 Magnum ammo. Anyway, .308 JSP does +50% extra damage at no drawback, and the ammo is super cheap and really easy to craft. WIth this ammo, you'll be doing 98 damage per shot. Again, I just don't see how Trail Carbine even comes close to this level of damage. We're talking about a 74% damage improvement here, not some insignificant number :/
On top of all of this, This Machine's rate of fire is 2.14 shots per second, while Trail Carbine is 1.85 shots per second. So it's natural DPS is going to be even lower.
Basically I've shown that in every way, This Machine is superior... so again, I don't see why I should mention Trail Carbine.
I hope I've answered all of your criticisms.