lol - lets see here - mercedes benz have been using CV joints in the rear of their cars since the 70s. they also didnt use grease but filled gear oil in the CV joint.
usual life experienced by owners is about 30 years..
yes - it does not go into more aggressive angles like a FWD car - but the CV joint itself is a pretty remarkable design. Now lets take into consideration how it works, when the spline stub axle on the outside is in perfect plane to the shaft driving the joint assembly the whole assembly is stalled and just rotating as a whole item. it only starts to work - the balls move in and out of the joint's cup grooves when the stub axle plane changes relative to the axle, This also works backwards too - e.g. when you let out the clutch the whole engine moves and the joint angle slightly changes, it immediately relaxes as the torque load diminshes. Also remember that the manufacturer designed the engine and mounts in a way that the engine can "rotate" around the axis of the axles coming out of the gearbox. Babbu and sheeda ustaad welding your "aasuum svaap" did not do that.
Now as you know how the joint works - please choose the correct lubricant for it. Gear oil is ideal but a bit too hardcore to handle in a cv specially if its not a sealed design like the old mercedes type metal can axle boots. The next best is a soft but extreme duty grease with about 10% moly content (this makes it super dark) - a polyurea thickener is ideal but lithium also works provided the base oil is not garbage.
The joint is a "slow" moving high pressure joint - its not a high speed item. When you add grease in it make sure its recommended by its manufacturer that its usable in CV joints - recommendation from the ustaad suspension walay is not good for this job.
also keep in mind the inner tripod type joint has needle bearings like the cups of a U joint, never use moly grease in there unless you like to change joints every year. It uses regular wheel bearing grease. In both boots - there is a specific quantity to be used, dont think that flooding the joint is good. If you fill it 100% the boot will burst from hydraulic pressure applied from the grease as it needs to expand when it heats up in normal operation.
As always - Please follow control specification and then comment on a failure. just like you argue with your boss on "sahee tareeqa" when he criticizes that you are a lazy bum. - the control specification here is the "sahee tareeqa". Deviating from it always results in unfamiliar problems.