Too much hidden information/inconsistency

Every wondered why when you have around 15% life steal, proc Blood Price on Aatrox, dealing a whole bunch of damage, but the health recovered doesnt seem to match the output? Well thats because Blood Price's bonus physical damage doesnt apply life steal. However Nasus's Siphoning Strike does apply life steal despite having the same function.

J4's passive, Martial Cadence's bonus damage doesnt apply life steal. Naut's passive, Staggering Blow does. The list goes on and on.

The only way a player would reliably know this kind of information is if they go outside the game itself and look it up online. Similar to what the game Destiny did but the major difference is that Destiny's case is story whereas League's case is game mechanics.

Now the only reason I know about this was because I had to go outside the game rather than the game itself telling me that this skill/passive doesnt apply life steal. If there wasnt outside information explaining what game should've explained already, then a bunch of people would have a drastically hard time understanding what does or doesnt work. Imagine new players playing the game and dealing with this. Expecting Kindred's passive to apply life steal because what makes them think it wouldnt?

Could Riot please add in a tooltip directly telling players that this does or doesnt apply life steal?

Now there are a few other hidden information and inconsistencies but the life steal mechanic is my biggest issue personally. Are there any others that you have an issue with?