I can consistently get lane cs from jungle with rengar now.
It's all about how efficiently and safely you take all cs available.
It isn't just about csing mechanics and wave control. It's also about anticipation, which leads into good wave control if you understand wave control as a concept. What I prioritize depends on the role I'm playing.
I'll throw out certain situations to clarify what I mean.
If I'm playing mid, I will usually try to build a lead on my opponent by pushing them out of lane and denying them as much as possible, while also taking every cs I can. I play a lot of Viktor mid, which makes it very easy. The same time, you want to avoid being harassed and avoid ganks, and it might be worth it to drop some cs for lane safety. I usually gauge how I'm doing at about 12 minutes, 18 minutes and 22 minutes to ensure I hit all the right powerspikes. 110 by 12 mins is when a lane is going well. 90 if it's going poorly or on the lower side of even. Any less than that, and I consider the lane mostly lost and focus on pushing when I can and roaming to build a lead some other way.
If I'm playing top, it really depends on what I'm playing. If I'm playing shyvana or maokai or some shit like that, usually I have perfect cs just from soaking waves. If I'm playing something like Rengar top, sometimes I sacrifice cs to get better lane positioning to zone my opponent out of the lane, or just straight up kill them depending on if they burn their cooldowns trying to reset the wave by bouncing it off of my turret. All in all, top lane really depends on the matchup. If you're playing something like gangplank, you need to get perfect cs to build the necessary lead to carry. It really depends on what you're playing.
As ADC, mechanics and wave control matter a lot more, because it's a duo lane and a long lane, so it can be very risky if you don't take care of yourself. I can play both very aggressively as an adc, as well as passive farmer, depending on how the opponent is playing. The idea is to try not to hard to force things but to also punish your opponent whenever they make a mistake.
As a jungler, farming efficiency is EXTREMELY important, more important than any other role imo. If you can soak a decent amount of farm as a jungler without denying anyone on your team anything, you are guaranteed to be stronger and more useful than the enemy jungler. Your jungle pathing, taxing, and soaking waves when no one else is there to soak it and when showing yourself won't hurt your team is the difference between a decent jungler and a great jungler.