You are wrong again - and this time twice. Trail Carbine isn't much better even at 75 skill. At 25 LLR wins clearly with better fire rate and crit multiplier. And .357 is way easier to acquire than .44.
With everything tricked out the Trail Carbine will have a DAM rating of 67 with -6DT. That DAM rating in contrast is exactly the same as a hunting rifle with JHP hand loads. LLR would be doing 52 with -3DT in the same situation. 15 points Damage and 3 points of armor penetration spreads looks pretty big to me. .44 Magnum ammo is more common than .308 rounds. Lack of ammo will never be an issue for the Trail Carbine. Maybe you are thinking .45-70 Gov't rounds here. Otherwise we're playing different games.
So what are the real advantages of the LLR? Lets see.
-Lower spread. That matters less than you would think.
-0.5x Critical Hit chance...With Sneak attack criticals being king and 100% guaranteed.
-0.5Wg less. Finally something that really matters.
Now let us take a peek at the Trail Carbine's advantages.
-Higher DAM (at any skill level)
-Higher DPS (at any skill level)
-Huge amount of HP (500) for a gun. Takes forever for it to degrade to 75% CND. Even the most lazy can keep it repaired without Jury Rigging.
-Found in Novac very early in the game. If following the plot much sooner than the LLR. Stealing it is also allot easier.