Explaining how rending works properly would generally be pretty good for players to figure it out.
Basically every weapon has a base rending value too. This is literally just rending% that applies to your bleed/fire effects too. Some weapons have a penetration bar, which actually just increases your rending% on yourself while the weapon is out. You can verify this by putting soulblaze/bleed on a crusher or flak armored target and swapping between various weapons. This is ontop of how some attacks will have an additional rending modifier applied ontop specific to those attacks.
This obviously also means that on weapons with very very low base rending you get way more out of the stat since it “unlocks” more of the base damage, and weapons with higher base rending may not benefit much. It works as intended that way, but it would be cool if this was visualized in game somehow. A lot of people are convinced rending is terrible because they only ever tried it on a powersword.
It doesn’t help that Fatshark at some point erroneously claimed that rending past 100% makes for a substantial damage bonus. That doesn’t seem to work properly, you get some really tiny unnoticable damage bonus past 100%. Something like 2% more damage when you’re at 130% or something.