The final drive gear is exactly that, the final gear i.e it comes after all the other gears. It doesn't affect the other gears "mechanically", and is basically just a torque converter
A longer final drive (lower numerically) will be more durable than a shorter final drive in terms of the final drive breaking, but causes more radial loads due to the smaller diameter ring gear, and vice versa.
Let me reword that:
Longer Final Drive (e.g 3.7) - More durable, but increases radial loads
Shorter Final Drive (e.g 4.1) - Less durable, but decreases radial loads
Radial loads is what pushes the shafts apart, causing gear mesh misalignment and worn/cracked bearings, ultimately leading to increased tooth wear and/or breakages